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ASSOCIATION OF STRUCTURAL ENGINEERS
OF THE PHILIPPINES, INC.

NATIONAL
STRUCTURAL
CODE OF THE
PHILIPPINES
2015

VOLUME I

BUILDINGS, TOWERS, AND OTHER
VERTICAL STRUCTURES

PREFACE TO THE NSCP VOLUME 1, SEVENTH EDITION, 2015

Introduction

ASEP recognizes the need for an up-to-date structural code addressing the design and installation of structural systems
through requirements emphasizing performance. The new National Structural Code of the Philippines (NSCP Volume I) is
designed to meet these needs through various model codes/regulations, generally from the United States, to safeguard the
public health and safety nationwide.

This' updated Structural Code establishes minimum requirements for structural systems using prescriptive and
performance-based provisions. It is founded on broad-based principles that make possible the use of new materials and
new building designs. Also, this code reflects the latest seismic design practice for earthquake-resistant structures.

Changes and Developments

In its drive to upgrade and update the NSCP, the ASEP Codes and Standards Committee initially wanted to adopt the latest
editions of American code counterparts. However, for cases where available local data is limited to support the upgra e,
then some provisions and procedures of the NSCP 7'" edition were retained.

This NSCP 7th edition is referenced from the following:

a. Uniform Building Code UBC-1997

b. International Building Code IBC-2009

c. American Society of Civil Engineers ASCE/SEI 7-10

d. American Concrete Institute ACI3 1 8- 1 4M

e. American institute for Steel Construction AISC-05 with Supplementary Seismic Provisions

f American Iron and Steel Institute AIS1 S 1 00-2007

g. Reinforced Masonry Engineering Handbook of America

h. Concrete Masonry Handbook, 6th Edition

i. American National Standard Institute ANSI E1A/TIA-222-G-I-2007

j. American Society for Testing and Materials (ASTM) Standards

Significant revisions are summarized as follows:

a. Chapter 1 — General Requirements

The changes made in this chapter are the following:
a. 1 Section 1 02 - Definition of Failure
a.2 Section 1 03 - Classification of Structures

School buildings of more than one story, hospitals, designated evacuation centers, structures
are under the essential facilities category. Section 104 - Design Requirements

Churches, Mosque and other related religious structures are under the special occupancy
category Section 104-Design Requirements.

The provision for deflection of any structural member under the serviceability requirement is
deleted. This requirement for concrete and steel is specified in Chapters 4 and 5 respectively.

New requirements are added to the design review section.

a.3 Section 105 - Posting and Instrumentation

Association of Structural Engineers of the Philippines, Inc. (ASEP)

The provision of installed recording accelerograph is adjusted,

a.4 Inclusion of Appendix 1-A : Recommended Guidelines on Structural Design Peer Review of
Structures 2015

a.5 Inclusion of Appendix 1-B: Guidelines and Implementing Rules on Earthquake Recording
Instrumentation for Buildings

b. Chapter 2 - Minimum Design Loads

The changes made in this chapter are the following:

b. 1 Section 203 - Combination of Loads

The load factors and load combinations are revised particularly the load combinations
including wind load.

b.2 Section 205 - Live Loads

Additional loads are incorporated in the table for minimum uniform and concentrated loads
particularly the parking garage and ramp live load.

b.3 Section 207 - Wind Loads

Wind load provisions, which were previously based on ASCE7-05, are updated based on
ASCE7-10. In this edition, three different wind contour maps for the entire Philippine
archipelago are generated and provided for determining the basic wind speeds for different
categories of building occupancies as defined in Table 103-1. These maps provide basic wind
speeds that are directly applicable for determining pressures for design strength. Strength
design wind load factor is 1.0; whereas, allowable stress design wind load factor is 0.6.
Generally, basic wind speeds correspond to 3%, 7% and 15% probability of exceedance in 50
years (MRI = 1700,700 and 300 years, respectively). Four (4) permitted procedures in
determining the design wind loads for main wind-force resisting systems (MWFRS), for other
structures and building appurtenances and for components and cladding (C&C) are provided
such as;

® directional procedure for buildings of all heights,

© directional procedure for other structures and building appurtenances and
analytical procedure for components & cladding, and
© wind tunnel procedure

The ANSI EIA/TIA-222-G-2005 and ANSI EIA/TIA-222G-1-2007 are now fully referenced
for computing wind loads on steel antenna towers and antenna supporting structures.

b. 4 Section 208 - Earthquake Loads

The near-source factors for 2-km distance from a causative fault is included in addition to 5-
km, 10-km, 15-km distance and beyond 15-km distance.

ASCE/SEI 7-10, using spectral acceleration, is recognized as an alternative procedure in the
determination of the earthquake loads.

c. Chapter 3- Earthworks and Foundations

The revisions made in this chapter are the following:

c. 1 Provisions pertaining to the conduct and interpretation of foundation investigations for cases

involving liquefiable, expansive or questionable soils are adopted;

National Structural Code of the Philippines Volume l, 7th Edition, I s * Printing, 2016

c.2 The section on footings is amended to incorporate provisions for differential settlement,
design loads and vibratory loads;

c.3 The section on pile foundations is amended to incorporate new provisions on splicing of
concrete piles; and

c.4 The section on special foundations, slope stabilization and materials of construction are added.

c.5 Provisions for construction in Zone 4 pertaining to reinforcement of Precast Prestressed Piles
have been revised to ensure consistency with ACI 318.

c.6 The figure for cut slopes has been amended for clarity;

c.7 The figure for fill slopes has been amended for clarity and some provisions have been
modified;

c.8 A table on the minimum required number of boreholes has been added to the section on
foundation investigation;

c.9 Provisions pertaining to minimum dimensions of ditches have been modified;

c. 10 The section on excavations and fills has been amended to incorporate provisions for scouring
and erosion protection as well as support of excavations and open cuts;

c. 1 1 Provision pertaining to general pile requirements have been expand to include design of piles
and pile groups subjected to lateral loads.

c.12 A Section on MSE Structures and Similar Reinforced Embankments and Fills has been added.
Chapter 4 - Structural Concrete

To reflect the reorganization of ACI 318-14 which contained a number of significant technical changes, the
ASEP adopted similar changes in the NSCP 2015 7th Edition. The latest ACI 3 18 was reorganized as a member-
based document, i. e., particular member type, such as beam, column, or slab will have separate sub-sections for
all requirements to design that particular member type. This will eliminate the need to flip through several
Sections to comply with all the necessary design requirements for a particular structural member, as was
necessary with the old organization format.

d.l Section 401: General

General information regarding the scope and applicability of NSCP 2015, Vol. 1 is provided. Additional sub-
section on interpretation is included to help users better understand Chapter 4, Structural Concrete.

d.2 Section 402: Notation and Terminology

The definition for hoops has been modified because the use of interlocking headed bars is a concern regarding
the possibility that it will not be adequately interlocked and because the heads could become disengaged under
complex loadings well into the non-linear range of response. It is now defined as a closed tie oi continuously
wound tie, made up of one or several reinforcement elements, each having seismic hooks at both ends.

A definition for special seismic systems, a term used in Sections 418 and 419, has been added.

d.3 Section 403: Referenced Standards

The following referenced specifications have been added to Section 403.2.4:

* ASTM A370-14, Standard Test Methods and Definitions for Mechanical Testing of Steel Products
© ASTM A 1085- 13, Standard Specification for Cold-Formed Welded Carbon Steel Hollow
Structural Sections (PISS)

o ASTM C173/C173M-14, Standard Test Method for Air- Content of Freshly Mixed Concrete by
Volumetric Method

Association of Structural Engineers of the Philippines, Inc. (ASEP)

* ASTM C1582/CI582M-1 1, Standard Specification for Admixtures to Inhibit Chloride-
Induced Corrosion of Reinforcing Steel in Concrete

A new referenced specification from Australia and New Zealand, Section 403.2.6 is added. These
standards were included as ACI 3 1 8 has no provisions related to Qualifications on the Use of Quenched
Tempered QT/Thermo-Mechanically Treated Reinforcement, which are the type manufactured, sold,
and commonly used for building construction in the Philippines:

The following referenced specifications have been deleted:

© ASTM C109/C109M-08, Standard Test Method for Compressive Strength of Hydraulic
Cement Mortars (Using 50 mm Cube Specimens)

Several referenced standards and specifications have been updated, as in most cases with every edition
of the NSCP. Note that the edition of every referenced standard is important. The NSCP does not
necessarily adopt new editions of referenced standards unless they are vetted before the publication of
each edition of the standard.

d.4 Section 404: Structural System Requirements

This new Section has been added to Chapter 4 to introduce structural system requirements.
This Section contains Sub-sections on Materials, Design Loads, Structural System and Load
Paths, Structural Analysis, Strength, Serviceability, Durability, Sustainability, Structural
Integrity, Fire Resistance, Requirements for Specific Types of Construction, Construction and
Inspection, and Strength Evaluation of Existing Structures. Most of these Sub-sections refer to
the other Sections in the NSCP. The Sub-section on construction and inspection, for instance,
refers to Section 426. In the areas for Sustainability and Fire Resistance, the NSCP does not
have specific requirements. This Sub-section on Sustainability allows the licensed design
professional to specify in the construction documents, sustainability requirements in addition
to the strength, serviceability, and durability requirements of the NSCP. The strength,
serviceability, and durability requirements are required to take precedence over sustainability
considerations, though these requirements are generally in harmony with sustainable
structures. In the Sub-section on Fire Resistance, the NSCP refers to the fire-protection
requirements of the NSCP Chapter 4, Sub-section 420.6.1. However, if the National Building
Code of the Philippines requires a greater concrete cover, such greater thickness shall govern.

d,5 Section 405: Loads

The following modification has been made in the provision for live load reduction because
there are still unincorporated areas where there may not be included in the previous editions of
the NSCP. The 7 l)1 Edition, Sub-section 405.2.3 - Live load reductions shall be permitted in
accordance with the National Building Code of the Philippines, or in its absence, in
accordance with ASCE/SEI 7.

For many Code revision cycles, ACI 318 retained provisions for service-level earthquake
forces in the design load combinations. In 1993, ASCE/SEI 7 converted earthquake forces to
strength-level forces and reduced the earthquake load factor to 1.0, and the model building

National Structural Code of the Philippines Volume 1, 7th Edition, 1 st Printing, 2016

vii

codes followed suit. In modern building codes around the world, earthquake loads are now
strength-level forces. Any references to service-level earthquake forces have been deleted.

d.6 Section 406: Structural Analysis

The following new item has been added in Sub-section 406.6.2.3:

(b) For frames or continuous construction, it shall be permitted to assume the intersecting membei
regions are rigid.

Previous NSCP 6 th Edition has been silent on the use of finite element analysis (FEA), though it is now
frequently used. Sub-section 406.9 now has provisions that are intended to explicitly allow the use of
FEA and to provide a framework for the future expansion of FEA provisions, but not as a guide toward
the selection and use of FEA software. The new Sub-section on diaphragms and collectors makes
explicit reference to the use of FEA, which makes it imperative that the NSCP 7'” Edition recognize the
acceptability of its use.
d.7 Section 408: Two-Way Slabs

Sub-section 418.10.1 (corresponding to ACI 318M-1 1, Section 18.9.1), says that a minimum
area of bonded reinforcement shall be provided in all flexural members with unbonded
prestressing tendons. The purpose of the minimum unbonded reinforcement over the tops of
columns is to distribute cracking caused by high local flexural tensile stresses in areas ol peak
negative moments. However, the high local flexural tensile stresses are not unique to slabs
with unbonded tendons. The new reorganized Sub-section 408.6.2.3 (corresponding to ACI
318M-14 Section S.6.2.3) requires the same minimum reinforcement in slabs with unbonded
or bonded tendons, except that the area of bonded tendons is considered effective in
controlling cracking.

It was also decided by the ACI 318 Committee, that if the same bonded reinforcement were
required for both bonded and unbonded post-tensioned two-way systems, the structural
integrity requirements for both systems should also be the same. The structural integrity
requirements in ACI 318M-11, Section 18.12.6 applied to two-way post-tensioned slab
systems with unbonded tendons only. The structural integrity requirements in ACI 318M-14
Section 8. 7.5.6 (corresponding to the NSCP 2015, Sub-section 408.7.5.6) now apply to two-
way post-tensioned slab systems with bonded as well as unbonded tendons.

d.8 Section 409: Beams

The use of open web reinforcement for torsion and shear in slender spandrel beams by the
precast concrete industry as an alternative to the closed stirrups traditionally mandated by this
Code. Eliminating closed stirrups is desirable because they cause reinforcement congestion,
production costs also increase significantly because pre-tensioning strand must be threaded
through the closed stirrups.

A new relevant Sub-section 409.5.4.7 for solid precast sections is added to the NSCP 7 ,h
Edition.

d.9 Section 412: Diaphragms

For the first time, a new Section 412, added design provisions for diaphragms in buildings
constructed in areas of low seismicity (Zone 2) The new Section applies “to the design of non-
prestressed and prestressed diaphragms, including:

(a) . Diaphragms that are cast-in-place slabs

(b) . Diaphragms that comprise a cast-in-place topping slab on precast elements

Association of Structural Engineers of the Philippines, Inc. (ASEP)

viii

(c) . Diaphragms that comprise precast elements with end strips formed by either a cast-
in-place concrete topping slab or edge beams

(d) . Diaphragms of interconnected precast elements without cast-in-place concrete
topping

d.10 Section 418: Earthquake-Resistant Structures

There are a number of significant and substantive changes to this Section.

Column confinement - The ability of the concrete core of a concrete reinforced column to sustain compressive
strains tends to increase with confinement pressure. Confinement requirements for columns of special moment
frames, and for columns not designated as part of the seismic-force-resisting system in structures assigned to
seismic zone 4 (similar to ASCE 7-10 Seismic Design Categories D, E, and F), with high axial load or high
concrete compressive strength are significantly different.

Transverse reinforcement - One important new requirement for special moment frame columns are included in
Sub-sections 418.7.5.2 and 418.7.5.4. There are new restrictions on the use of headed reinforcement to make up
hoops.

Special moment frame beam-column joints - For beam-column joints of special moment frames, clarification of
the development length of the beam longitudinal reinforcement that is hooked, requirements for joints with
headed longitudinal reinforcement, and restrictions on joint aspect ratio are new. For beam-column joints of
special moment frames, clarification of development length of beam longitudinal reinforcement that is hooked,
requirements for joints with headed longitudinal reinforcement, and restrictions on joint aspect ratio are new.

Special shear walls - Subsection 418.10 (equivalent to AC1 31S-14M-14 Section 18.10, previously
ACI 318M-11 Section 21.9), has been extensively revised in view of the performance of buildings in the Chile
earthquake of 2010 and the Christchurch, New Zealand, earthquakes of 201 1, as wells as full-scale reinforced
concrete building tests. In these earthquakes and laboratory tests, concrete spalling and vertical reinforcement
buckling were at times observed at wall boundaries.

For ASTM A615 Grade 420 bars used as longitudinal reinforcement in special moment frames and special shear
wails, the NSCP 7 lh Edition now requires the same minimum elongation as ASTM A706 reinforcement.

d.ll Section 419: Concrete: Design and Durability Requirements

Quite a few changes have been made in concrete durability requirements, which are now located in this Section.

d.12 Section 420: Steel Reinforcement Properties, Durability and Embedments

The definition of yield strength of high-strength reinforcement for Grade 420 (Grade 60) in this Section is now,
for the first time, the same as that in ASTM specifications, except for bars with less than 420 MPa, the yield
strength shall be taken as the stress corresponding to a strain of 0.35 percent.

Delormed and plain stainless steel wire and welded wire conforming to ASTM A 1 022 is now permitted to be
used as concrete reinforcement.

Sub-section 420.2.2.5 requires “Deformed non-prestressed longitudinal reinforcement resisting earthquake
moment, axial force, or both, in special moment frames, special structural walls, and all the components of
special structural walls including coupling beams and wall piers” to be ASTM A706 Grade 420 (Grade 60),
ASTM 615 Grade 275 (Grade 40) or Grade 420 (Grade 60) reinforcement is permitted if two supplementary
requirements are met, which are already part of the ASTM A706 specification. A third supplementary
requirement is now added for ASTM A615 (Grade 60) reinforcement to be permitted for use in special moment
frames, special structural walls. The minimum elongation in 200 mm (8”) must now be the same as that ASTM
A615 (Grade 60) reinforcement.

One aspect of the Code compliance that the Association of Structural Engineers of the Philippines is cautioning
Designers and Constructors alike, is the introduction of ASTM 615 Grade 520 (Grade 75) in the Philippine

National Structural Code of the Philippines Volume 1, 7th Edition, 1 st Printing, 2016

market. Since this was not covered by previous editions of the NSCP Vol. 1, it creates an impression of an
unregulated use of a new high-strength reinforcement grade. NSCP 7 1 Ed.t.on,

To put it clearly, Sub-section 420.2.2.5, corresponding to ACI 3 18M-14 Section 20.2.2.5, specifies the
use of deformed non-prestressed longitudinal reinforcement resisting earthquake-induced moment,
axial force, or both, in special moment frames, special structural walls, and all components of special
structural walls, including coupling beams, and wall piers which shall be in accordance with (a) or (b):

(a) . ASTM A706M, Grade 420

(b) . ASTM A615M, Grade 280

There was no mention that ASTM A615M, Grade 520, was allowed, although the use of micro-alloyed
high-strength reinforcement may be allowed in the future through the issuance of a new ASTM or
updated standard, and with proper validation by the Department of Trade and Industry s Bureau ot
Standards. It will be premature to allow its use for special moment frames, special structural walls, and
all components of special structural walls, including coupling beams, and wall piers tor Buildings
located in areas of high seismicity (zone 4). The same restrictions indicated in Sub-section 420.7.6, on
the use of quenched-tempered thermo-mechanically treated (QT/TMT) reinforcing bars in structures
located in seismic zone 4 for Grade 420 reinforcement, shall also be applied to Grade 520, unless
proven in subsequent studies and tests.

d.13 Section 422: Sectional Strength
The following are the changes in Section 422:

For prestressed members, a new equation for the nominal axial strength at zero eccentricity has been
introduced in Sub-section 422.4*2.3.

New Sub-section 422.4.3*1, which requires that the nominal axial tensile strength of a non-prestressed,
composite, or prestressed member, not to be taken greater than the maximum nominal axial tensile
strength of member.

d.14 Section 425: Reinforcement Details

Two changes shown in Table 7 (part of Table 425. 3.2) are made to eliminate the differences between
the required tail extension of a 90-degree or 135- degree standard hook, subject to a minimum of 75
mm (3”).

Mechanical or welded splices with strengths below 125% of the yield strength ol the spliced reinfoicing
bars are no longer permitted. The associated stagger requirements have been deleted. Thus there is no
longer a need to specify “full” mechanical or “full’ welded splices.

d.15 Section 426: Construction Documents and Inspection

In this section, the user will probably require some time to get used to, it starts with the following:

426.1.1 This Sub-section addresses (a) through (c):

(a) Design information that the licensed design professional shall specify in the construction
documents,

(b) Compliance requirements that the licensed design professional shall specify in the
construction documents,

Thus, construction and inspection requirements have been consolidated, and they are now related to
construction documents. The construction requirements are designated either as “design information” or
“compliance requirements.” These are largely existing material that has been rearranged. The

Association of Structural Engineers of the Philippines, Inc. (ASEP)

inspection requirements in Sub-section 426.13 are taken from Chapter 17 of the 2015 International
Building Code (IBC) and were previously not part of ACI 318.

Provisions in ACI 318-11 and earlier editions, which explained basic statistical considerations
in mixture proportioning, are no longer found in ACI 318-14. Instead, ACI 301-10,
Specifications for Structural Concrete , is referenced.

These are some other changes in the makeup of NSCP 2016 7 th Edition that should be noted:

1 . There are two new Sections: Section 404, Structural System Requirements and
Section 412, Diaphragms.

2. Section 422, Structural Plain Concrete, now Section 414.

3. Section 423, Anchoring to Concrete, is now Section 417, with no significant
changes.

4. Section 42 1 , Earthquake-Resistant Structures, now Section 418.

5. Section 427, Strut-and-Tie Models is now Section 423, with no significant
changes.

6. Section 420, Strength Evaluation of Existing Structures, is now Section 427.

7. Section 419, Shells and Folded Plates, is now Section 428.

8. Section 424, Alternative Design Method, now Section 429, is adapted from
earlier editions of the NSCP.

9. Section 425, Alternative Provisions for Reinforced and Prestressed Concrete
Flexural and Compression Members, and Section 426, Alternative Load and
Strength Reduction Factors, have been discontinued.

10. On the other hand. Section 416, Precast Concrete, and Section 418, Prestressed
Concrete, no longer exist as separate entities. The provisions of these Sections
are now spread over several of the new Sections.

Sub-section 418.18, Requirements for post-tensioning ducts and grouting have also been removed as
being outdated. The Commentary now provides specification guidance.

e. Chapter 5: Structural Steel.

ASEP adapted the American Institute of Steel Construction (AISC) 14th Edition in this updated
Structural Steel code. The revisions made in this chapter are the following:

e.l The entire Structural Steel chapters are streamlined placing all chapter definitions under one
Definition heading, tables are immediately shown where they are first mentioned, figures drawn
larger, equation are all in boldface, extraneous user notes are removed, essential in-text definitions
italicized and in-text equation terms are written in boldface for easy reference.

e.2 Change of headings and terms.

501.3.5 Filler Metal and Flux for Welding to 501.3.5 Consumables for Welding
510.10.3 Web Crippling to Web Local Crippling

557.5 Special Fabrication Requirements. Weld tabs changed to Run-off tabs under
Exception.

A-6.3 Beams changed to Beams Bracing

e.3 Creation of new subtopic.

APPENDIX A -4

National Structural Code of the Philippines Volume 1, 7th Edition, 1 st Printing, 2016

STRUCTURAL FIRE f

A -4.2.3. 1 Thermal Elongation is created under A-4.2.3 Material Strengths at Elevated

Temperatures
APPENDIX A-6

STABILITY BRACING FOR COLUMNS AND BEAMS
A-6.4 Beam-Column Bracing

SECTION 529 BUCKLING-RESTRAINED BRACED FRAMES (BRBF)

A section 529.3 was created as heading for 529.3.1 and 529.3.2

e.4 Revision in load factor

5 10.8 Column Bases and Bearing on Concrete

2010- n c =2.5(/(SD)

2015: 0c = 0.65(LRFD) = 2. 31(4SD)

e.5 Revision in equations

B-5. QUALIFYING CYCLIC TESTS OF BUCKLING-RESTRAINED BRACES
51 1.2.2c Branches with Axial Loads in K-Connections

2010 :

Q s =r l

1 +

0 , 24 /"

•frH * 1

(5M.2-7) Q z

; 2015:

0.24 Y 12 \

c IV-v’hJ

(5H>7)

APPENDIX A-3 - DESIGN FOR FATIGUE
A-3.4 Bolts and Threaded Parts

A, -$(</„ -9382 ) 2 At = f id b - 0-9382 P)*

2010: 4 ; 2015:

Chapter 6: Wood.

The revisions made in this Chapter are the following:

f.l Section 616 - Design Provisions and Equations: The NDS 2015 Chapter 3 is adopted
almost in its entirety;

f.2 Section 6 1 7 - Sawn Lumber: The NDS 20 1 5 Chapter 4 is adopted almost in its entirety;

f.3 Section 618 - Structural Glued Laminated Timber: The NDS 2015 Chapter 5 is adopted

almost in its entirety;

f.4 Tables 619.1-3 and 6 1 9. 1 -4 are revised based on NDS 20 1 5; and

f.5 Other Sections affected are adj usted accordingly.

Chapter 7: Masonry

The revisions made in this chapter are the following:

g. 1 The specified yield strength of steel reinforcement is 420MPa instead of 413 MPa / 415 MPa;

Association of Structural Engineers of the Philippines, Inc. (ASEP)

xii

g.2 Section 710.6.3 and Section 710.7.1

10mm diameter instead ofNo.9 gage wire

g.3 Section 713.9.1

20mm diameter instead of 19-gage
25 mm diameter instead of 24-gage

3. Acknowledgment

The ASEP Codes and Standards Committee are indebted to Philippine Institute of Volcanology and Seismology
(PHIVOLCS) and to Dir. Renato V. Solidum, Ph. D. for his unselfish contribution specifically on Section 208 of
this code.

ASEP acknowledges the contribution of Dr. Teresito C. Bacolcol and Ms. Madeline Cabologan of PHIVOLCS for
the seismic maps used in this code.

ASEP acknowledges the contribution of Engr. Carlos M. Villaraza for his unselfish contribution on Chapter 2
Seismic/Earthquake Chapter.

The contributions of ASEP members and other users of this code who have suggested improvements, identified
errors and recommended items are recognized.

ASEP also acknowledges the contribution of the industry partners, companies and individuals, who continue to
support ASEP’s numerous undertakings.

The ASEP Codes and Standards Committee also acknowledge Arch. Avigaile Genota Riola who designs the covers
of the NSCP Volume 1, 2010 Edition and NSCP Volume 1, 2015 Edition.

National Structural Code of the Philippines Volume I, 7th Edition, 1 st Printing, 2016

xiii

Suite 713, Future Point Plaza Condominium 1
112 Fanay Avenue, Quezon City, Philippines 1100

Tel* No. : (+632) 410-0483
Fax No* : (+632) 411-8606
Email: aseponl in e@gmai I .com
Website:http://ww\v*aseponline.org

National Structural Code of the Philippines Volume ! ? 7th Edition, 2015

CHAPTER 1 - General Requirements 1-1

Table of Contents

SECTION 101

TITLE, PURPOSE AND SCOPE

101.1 Special Foundation Systems 2

101.2 Purpose 2

101.3 Scope

1 0 1.4 Alternati ve Systems 2

SECTION 102

DEFINITIONS

SECTION 103

CLASSIFICATION

OF STRUCTURES

103.1 Nature of Occupancy q

SECTION 104

DESIGN REQUIREMENTS

104.1 Strength Requirement 7

1 04.2 Serviceability Requirement

104.3 Analysis 7

1 04.4 Foundation Investigation g

104.5 Design Review g

SECTION 105

POSTING AND INSTRUMENTATION

105.1 Posting of Live Loads

105.2 Earthquake-Recording Instrumentation 9

SECTION 106

SPECIFICATIONS, DRAWINGS AND CALCULATIONS

1 06. 1 General * 9

106.2 Specifications * „ . 9

1 06.3 Design Drawings 9

SECTION 107

STRUCTURAL INSPECTIONS, TESTS AND STRUCTURAL OBSERVATIONS 10

107.1 General jq

107.2 Definitions jq

107.3 Structural Inspector jq

107.4 Inspection Program j j

1 07.5 Types of Work for Inspection I \

107.6 Approved Fabricators j3

107.7 Prefabricated Construction j 3

107.8 Non-Destructive Testing 14

1 07.9 Structural Observation j 5

APPENDICES

LA - Recommended Guidelines on Structural Design Peer Review of Structures 2015 IA-1

LA - Guidelines and Implementing Rules on Earthquake Recording Instrumentation for Buildings IB-1

National Structural Code of the Philippines Volume I, 7th Edition, 2015

1-2 CHAPTER 1 - General Requirements

iiiWiiM it# ; > \

IpilllPtiRPOSE AND SCOPE .11111)

101.1 Special Foundation Systems

These regulations shall be known as the National
Structural Code of the Philippines 2015, Volume I, 7th
Edition, and may be cited as such and will be referred to
herein as ‘'Ibis code."

101.2 Purpose

The purpose of this code is to provide minimum
requirements for the design of buildings, towers and other
vertical structures, and minimum standards and guidelines
to safeguard life or limb, property and public welfare by
regulating and controlling the design, construction,
quality of materials pertaining to the structural aspects of
all buildings and structures within this jurisdiction.

101.3 Scope

The provisions of this code shall apply to the construction,
alteration, moving, demolition, repair, maintenance and use
of buildings, towers and other vertical structures within this
jurisdiction.

Special structures such as but not limited to single family
dwellings, storage silos, liquid product tanks and
hydraulic flood control structures, should be referred to
special state of practice literature but shall refer to
provisions of this code as a minimum wherever
applicable.

For additions, alterations, maintenance, and change in use
of buildings and structures, see Section 108.

Where, in any specific case, different sections of this code
specify different materials, methods of construction or
other requirements, the most restrictive provisions shall
govern except in the case of single family dwellings. Where
there is a conflict between a general requirement and a
specific requirement, the specific requirement shall be
applicable.

101.4 Alternative Systems

The provisions of this code are not intended to prevent the
use of any material, alternate design or method of
construction not specifically prescribed by this code,
provided any alternate has been permitted and its use
authorized by the Building Official (see Section 102).

Sponsors of any system of design or construction not
within the scope of this code, the adequacy of which had
been shown by successful use and by analysis and test,
shall have the right to present the data on which their
design is based to the Building Official or to a board of
examiners appointed by the Building Official or the project
owner/developer. This board shall be composed ot
competent structural engineers and shall have authority to
investigate the data so submitted, to require tests if any, and
to formulate rules governing design and construction of
such systems to meet the intent of this code. These rules,
when approved and promulgated by the Building Official,
shall be of the same force and effect as the provisions of
this code

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 1 - General Requirement 1-3

For the purpose of this code, certain terms, phrases, words
and their derivatives shall be construed as specified in this
chapter and elsewhere in this code where specific
definitions are provided. Terms, phrases and words used in
the singular include the plural and vice versa. Terms,
phrases and words used in the masculine gender include the
feminine and vice versa.

The following terms are defined for use in this code:

ALTER or ALTERATION is any change, addition or
modification in construction or occupancy.

APPROVAL shall mean that the proposed work or
completed work conforms to this code in the opinion of the
Building Official.

APPROVED as to materials and types of construction,
refers to approval by the Building Official as the result of
investigation and tests conducted by the Building Official,
or by reason of accepted principles or tests by recognized
authorities, technical or scientific organizations.

AS GRADED is the extent of surface conditions on
completion of grading.

AUTHORITY HAVING JURISDICTION is the
organization, political subdivision, office or individual
charged with the responsibility of administering and
enforcing the provisions of this code.

BEDROCK is in-place solid or altered rock.

BENCH is a relatively level step excavated into earth
material on which fill is to be placed.

BORROW is earth material acquired from an off-site
location for use in grading on a site.

BUILDING is any structure usually enclosed by walls
and a roof, constructed to provide support or shelter for an
intended use or occupancy.

BUILDING OFFICIAL is the officer or other designated
authority charged with the administration and enforcement
of this code, or the Building Official’s duly authorized
representative.

CIVIL ENGINEER is a professional engineer licensed to
practice in the field of civil engineering.

CIVIL ENGINEERING is the science or profession in
which a knowledge of the mathematical and physical
sciences gained by study and practice is applied with
judgement to utilize natural and man-made resources and
forces in the planning, design, management, construction,
and maintenance of buildings, structures, facilities, and
utilities in their totality, for the progressive well-being and
for the benefit of mankind, enhancing the environment,
community living, industry, and transportation, taking into
consideration such aspects as functionality, efficiency,
economy, safety, and environmental quality.

COMPACTION is the densification of a fill by
mechanical or chemical means.

CONSTRUCTION FAILURE is a failure that occurs
during construction and they are considered to be either a
collapse or distress, of a structural system to such a degree
that it cannot safely serve its intended purpose . 1

CONTINUOUS STRUCTURAL INSPECTION is a
structural inspection where the structural inspector is on the
site at all times observing the work requiring structural
inspection.

EARTH MATERIAL is any rock, natural soil or fill or
any combination thereof.

ENGINEER-OF-RECORD is a civil engineer responsible
for the structural design.

EROSION is the wearing away of the ground surface as a
result of the movement of wind or water.

EXCAVATION is the mechanical removal of earth
material.

EXISTING GRADE is the grade prior to grading.

BUILDING, EXISTING is a building erected prior to the FAILURE is defined as an unacceptable difference

ac option of this code, oi one for which a legal between expected and observed performance. This

building permit has been issued. definition includes catastrophic structural collapse, but also

includes performance problems that are not necessarily
catastrophic or life-threatening, including “serviceability
problems such as distress, excessive deformation,
premature deterioration of materials, leaking roofs and
facades, and inadequate interior environmental control
systems.” In the event of a significant failure, the parties
typically retain experts to determine the cause of the
perceived failure. Occasionally a failure results from a
National Structural Code of the Philippines Volume 1, 7th Edition, 2015

1-4 CHAPTER 1 - Genera! Requirements

single condition, but typically, failures result from a
combination of mistakes, oversights, miscommuni cations,
misunderstandings, ignorance, lapses, slips, incompetence,
intentional violations or non-compliance, and inadequate
quality assurance. The causes for these conditions vary, but
may include simple mistakes (such as sending information
to a structural engineer when it should have been sent to the
architect), conclusions based on faulty assumptions, an
employee's “laziness, ignorance, or malevolent urge,
fatigue from excessive workload, inadequate training, “time
boxing'' practices used to minimize fees to a client,
overreliance on computer-aided design and drafting
(CADD), failure to understand and deliver client
requirements, time pressures to a deliver a project by
certain deadlines, and ineffective coordination and
integration of the design team . 2

FILL is a deposit of earth material placed by artificial
means.

FINISH GRADE is the final grade of the site that
conforms to the approved plan.

FORENSIC ENGINEERING is the application of the art
and science of engineering in the jurisprudence system,
requiring the services of legally qualified engineers.
Forensic engineering may include investigation of the
physical causes of accidents and other sources of claims
and litigation, preparation of engineering reports, testimony
at hearings and trials in administrative or judicial
proceedings, and the rendition of advisory opinions to
assist the resolution of disputes affecting life or property/

GENERAL COLLAPSE is the immediate, deliberate
demolition of an entire structure by a triggering event (e.g,
explosion)/ 7

GEOTECHNICAL ENGINEER is a registered Civil
Engineer with special qualification in the practice of
Geotechnical Engineering as recognized by the Board of
Civil Engineering of the Professional Regulation
Commission as endorsed by the Specialty Division of
Geotechnical Engineering of the Philippine Institute of
Civil Engineers (PICE).

GEOTECHNICAL ENGINEERING is the application of
the principles of soil and rock mechanics in the
investigation, evaluation and design of civil works
involving the use of earth materials and foundations and the
inspection or testing of the construction thereof

GRADE is the vertical location of the ground surface.

GRADING is an excavation or fill or combination thereof

KEY is a designed compacted fill placed in a trench
excavated in earth material beneath the toe of a slope.

LIMITED LOCAL COLLAPSE is a failure of a
structural member without affecting the adjacent members
(e.g. destruction of one or two columns in a multi-bay
structure)/

OCCUPANCY is the purpose for which a building or
other structures or part thereof, is used or intended to be
used.

PERIODIC STRUCTURAL INSPECTION is a
structural inspection where the inspections are made on a
periodic basis and satisfy the requirements of continuous
inspection, provided this periodic scheduled inspection is
performed as outlined in the inspection program prepared
by the structural engineer.

PREFABRICATED ASSEMBLY is a structural unit, the
integral parts of which have been built up or assembled
prior to incorporation in the building.

PROFESSIONAL INSPECTION is the inspection
required by this code to be performed by the civil engineer.
Such inspections include that performed by persons
supervised by such engineer and shall be sufficient to form
an opinion relating to the conduct of the work.

PROGRESSIVE COLLAPSE is the spread of an initial
local failure from element to element, eventually resulting
in the collapse of an entire structure or disproportionately
large part o f it . 4

ROBUSTNESS is the insensibility of a structure to local
failure. From this definition, it follows that the robustness
is a property of the structure/

ROUGH GRADE is the stage at which the grade
approximately conforms to the approved plan.

SITE is any lot or parcel of land or contiguous combination
thereof, under the same ownership, where grading is
performed or permitted.

SLOPE is an inclined ground surface the inclination of
which is expressed as a ratio of vertical distance to
horizontal distance.

SOIL is naturally occurring superficial deposits overlying
bedrock.

SOILS ENGINEER See Geotechnical Engineer.

SOILS ENGINEERING See Geotechnical Engineering,

STRUCTURE is that which is built or constructed, an
edifice or building of any kind, or any piece of work
artificially built up or composed of parts joined together in
some definite manner.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 1 - Genera! Requirement 1-5

STRUCTURAL ENGINEER is a registered Civil
Engineer with special qualification in the practice of
Structural Engineering as recognized by the Board of Civil
Engineering of the Professional Regulation Commission or
by the Specialty Division of the Philippine Institute of Civil
Engineers (PICE) together with the Association of
Structural Engineers of the Philippines (ASEP) and
Institution of Specialist Structural Engineers of the
Philippines (ISSEP).

STRUCTURAL ENGINEERING is a discipline of civil
engineering dealing with the analysis and design of
structures that support or resist loads insuring the safety of
the structures against natural forces.

STRUCTURAL FAILURE is the reduction of capability
of a structural system or component to such a degree that it
cannot safely serve its intended purpose. 5

Structural failures can be divided into various categories
based on consequential damages to include: Catastrophic
Failure with Loss of Life, Catastrophic Failure in which No
Human Lives are Endangered, Failure Resulting in
Extensive Property Damage, and Failure Resulting in
Reduced Serviceability. 5

STRUCTURAL INSPECTION is the visual observation
by a structural inspector of a particular type of construction
work or operation for the purpose of ensuring its general
compliance to the approved plans and specifications and
the applicable workmanship provisions of this code as well
as overall construction safety at various stages of
construction.

STRUCTURAL OBSERVATION is the visual
observation of the structural system by the structural
observer as provided for in Section 107.9.2, for its general
conformance to the approved plans and specifications, at
significant construction stages and at completion of the
structural system. Structural observation does not include
or waive the responsibility for the structural inspections
required by Section 107. 1 or other sections of this code.

TERRACE is a relatively level step constructed in the
face of a graded slope surface for drainage and maintenance
purposes.

* Guide to Investigation of Structural Failures, ASCE, 1986.

" The American Society of Civil Engineers (ASCE) Technical Council on
Forensic Engineering.

forensic Engineering,, T d Edition, KenethL Carper, Editor, 200 J.

Robustness of Buildings in Structural Codes , Dimitris Diamantidis,

2009

Structu ral Failures in Buildings, ASCE, 1981.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

1-6 CHAPTER 1 - General Requirements

.OF STRUCTURES

103.1 Nature of Occupancy

Buildings and other structures shall be classified, based on
the nature of occupancy, according to Table 103-1 tor
purposes of applying wind and earthquake loads in Chapter
2. Each building or other structures shall be assigned to the
highest applicable occupancy category or categories.
Assignment of the same structure to multiple occupancy
categories based on use and the type of loading condition
being evaluated (e.g. wind or seismic) shall be permissible.

When buildings or other structures have multiple uses
(occupancies), the relationship between the uses of various
parts of the building or other structure and the
independence of the structural system for those various
parts shall be examined. The classification for each
independent structural system of a multiple-use building or
other structure shall be that of the highest usage group in
any part of the building or other structure that is dependent
on that basic structural system.

Table 103-1 Occupancy Category

OCCUPANCY

OCCUPANCY OR FUNCTION OF

Category

1 . Access floor systems

2. Armories

3. Theaters,
assembly
areas 3 and
auditoriums

4. Bowling alleys, poolrooms

and similar recreational
areas

5. Catwalk for maintenance
access

6, Cornices and marquees

7. Dining rooms and restaurants

8. Exit facilities 5

9* Parking Garages and Ramps

10. Hospitals

1 1 . Libraries

12. Manufacturing

Description

Office use

Computer use

Fixed seats
Movable seats
Lobbies and platforms
Stage areas

General storage and/or repair

Public parking and ramps

Private (residential) or pleasure-
type motor vehicle storage

Wards and rooms

Laboratories and operating rooms

Corridors above ground floor
Reading rooms
Stack rooms

Corridors above ground floor
Light
Heavy

Building corridors above ground
floor

Uniform Load 1
kPa

Concentrated Load

9.0 2

O 6

t-x

— 7

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-17

Table 205-1 Minimum Uniform and Concentrated Live Loads ( continued)

Use or Occupancy

Uniform Load 1

Concentrated Load

Category

Description

kPa

••

Call centers and business processing
offices

2.9

9.0

13, Office

Lobbies and ground floor corridors

4.8

9.0

Other offices

2.4

9.0-

: 14. Printing plants

Press rooms

7.2

11.0-

Composing and linotype rooms

4.8

9.0 2

Basic floor area

1.9

0 s

. 15. Residential*

Exterior balconies

2.9 4

Decks

1.9 4

Storage

1.9

16. Restrooms 9

1 1. Reviewing stands,

grandstands, bleachers, and
folding and telescoping seating

4.8

18. Roof decks

Same as area served or occupancy

Classrooms

1.9

4,5“

19. Schools

Corridors above ground floor

3.8

4.5

i nr

Ground floor corridors

4.8

4.5

20. Sidewalks and driveways

Public access

12.0

__ 7

21. Storage

Light

6.0

Heavy

12,0

22. Stores

Retail

4.8

4.5 2

Wholesale

6.0

13.4 2

23. Pedestrian bridges and
walkways

4.8

Notes for Table 205- 1

1 See Section 2 05. 5 for li ve load reductions.

See Section 205.3.3 , first paragraph , for area of load
application.

' Assembly areas include such occupancies as dance halls , drill
rooms, gymnasiums, playgrounds, plazas, terraces and similar
occupancies that are generally accessible to the public.

4 For special-purpose roofs, see Section 205. 4. 4.

5 Exit facilities shall include such uses as corridors serving an
occupant load of 10 or more persons, exterior exit balconies,
stairways t fire escapes and similar uses.

Individual stair treads shall be designed to support a 1.3 N
concentrated load placed in a position that would cause
maximum stress. Stair stringers may be designed for the
uniform load set forth in the table.

See Section 205.3.3, second paragraph , for concentrated
loads . See Table 205-2 for vehicle barriers.

Residential occupancies include private dwellings, apartments
and hotel guest rooms.

Restroom loads shall not be less than the load for the
occupancy with which they are associated, but need not exceed
2.4 kPa.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-18 CHAPTER 2 - Minimum Design Loads

Table 205-2 Special Loads 1

Use or Occupancy

Vertical Load

Lateral Load

Category

Description

kPa

1 . Construction, public access at site (live
load)

Walkway

7.2

Canopy

7.2

2. Grandstands, reviewing stands,

bleachers, and folding and telescoping
seating (live load)

Seats and footboards

1 .75 2

See Note 3

3, Stage accessories (live load)

Catwalks

1.9

Follow spot, projection
and control rooms

2.4

4, Ceiling framing (live load)

Over stages

1.0

All uses except over
stages

0.5 4

5. Partitions and interior walls,

0.25

6. Elevators and dumbwaiters (dead and
live loads)

2*total load

7. Cranes (dead and live loads)

Total load including
impact increase

1 .25*tota! load^

0.10*total load 6

8. Balcony railings and guardrails

Exit facilities serving an
occupant load greater
than 50 persons

0.75 kN/m 7

Other than exit facilities

0.30 kN/m 7

Components

1.2®

9. Vehicle barriers

27 kN ?

10. Handrails

See Note 10

11. Storage racks

Over 2.4 m high

Total loads”

See Table 208-13

12. Fire sprinkler structural support

1.1 kN plus weight of
water-filled pipe”’

See Table 208-13

Notes for Table 205-2

1 The tabulated loads are minimum loads. Where other vertical loads required by the design would cause greater stresses, they shall be used. Loads are in kPa unless
otherwise indicated in the table.

' Units is kN/m.

i Lateral sway bracing loads of 3 50 N/m parallel and 145 N/m perpendicular to seat and footboards.

4 Does not apply to ceilings that have sufficient access from below, such that access is not required within the space above the ceiling . Does not apply to ceilings if the attic
areas above the ceiling are not provided with access. This live had need not be considered as acting simultaneously with other live loads imposed upon the ceiling framing
or its supporting structure.

•' The impact factors included are for cranes with steel wheels riding on steel rails. They may be modified if substantiating technical data acceptable to the building official
is submitted Live loads on crane support girders and their connections shall be taken as the maximum crane wheel loads. For pendant-operated traveling crane support
girders and their connections, the impact factors shall be i. /ft

* This applies in the direction parallel to the runway rails (longitudinal). The factor for forces perpendicular to the rad is 0.20 * the transverse traveling loads (trolley, cab ,
books and lifted loads). Forces shall be applied at top of rail and may be distributed among rails of multiple rail cranes and shall he distributed with due regard for lateral
stiffness of the structures supporting these rails.

? A load per lineal meter (kN/m) to be applied horizontally at right angles to the top rail.

tt Intermediate rails , panel fillers and their connections shall be capable of withstanding a load of 1. 2 kPa applied horizontally at right angles over the entire tributary area,
including openings and spaces between rails. Reactions due to this loading need not be combined with those of Note 7.

9 A horizontal load applied at right angles to the vehicle barrier at a height of 450 mm above the parking surface . The force may be distributed over a 300-mm square.

t0 The mounting of handrails shall be such that the completed handrail and supporting structure are capable of withstanding a load of at least 890 N applied in any direction
at any point on the rail. These loads shall not be assumed to act cumulatively with Note 9.

Vertical members of storage racks shall be protected from impact forces of operating equipment, or racks shall be designed so that failure of one vertical mem be) will not
came collapse of more than the bay or bays directly supported by that member.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-1 9

/’ The / I~kN had is to be applied to any single fire sprinkler support point but not simultaneously to all support joints.

205.4 Roof Live Loads 205.4.4 Special Roof Loads

205.4.1 General

Roofs shall be designed for the unit live loads, L r , set forth
in Table 205-3. The live loads shall be assumed to act
vertically upon the area projected on a horizontal plane.

205.4.2 Distribution of Loads

Where uniform roof loads are involved in the design of
structural members arranged to create continuity,
consideration may be limited to full dead loads on all spans
in combination with full roof live loads on adjacent spans
and on alternate spans.

Exception:

Alternate span loading need not be considered where the
uniform roof live load is 1.0 kPa or more ,

For those conditions where light-gage metal preformed
structural sheets serve as the support and finish of roofs,
roof structural members arranged to create continuity shall
be considered adequate if designed for full dead loads on
all spans in combination with the most critical one of the
following superimposed loads:

|l| ; The uniform roof live load, L r , set forth in Table 205-
IS 3 on all spans.

2. A concentrated gravity load, L r , of 9 kN placed on any
span supporting a tributary area greater than 1 8 nr to
HI' create maximum stresses in the member, whenever
H. this loading creates greater stresses than those caused
by the uniform live load. The concentrated load shall
be placed on the member over a length of 0.75 m along
the span. The concentrated load need not be applied to
more than one span simultaneously.

§3* Water accumulation as prescribed in Section 206.7.

205.4.3 Unbalanced Loading

Unbalanced loads shall be used where such loading will
result in larger members or connections. Trusses and
arches shall be designed to resist the stresses caused by unit
Jive loads on one-half of the span if such loading results in
reverse stresses, or stresses greater in any portion than the
stresses produced by the required unit live load on the
entire span. For roofs whose structures are composed of a
stressed shell, framed or solid, wherein stresses caused by
any point loading are distributed throughout the area of the
shell, the requirements for unbalanced unit live load design
may be reduced 50 percent.

Roofs to be used for special purposes shall be designed for
appropriate loads as approved by the building official
Greenhouse roof bars, purlins and rafters shall be designed
to carry a 0.45 kN concentrated load, L r , in addition to the
uniform live load

205.5 Reduction of Live Loads

The design live load determined using the unit live loads as
set forth in Table 205-1 for floors and Table 205-3, Method
2, for roofs may be reduced on any member supporting
more than 15 nr, including flat slabs, except for floors in
places of public assembly and for live loads greater than
4.8 kPa, in accordance with the following equation:

R = r(A ~~ 15 ) (205-1)

The reduction shall not exceed 40 percent for members
receiving load from one level only, 60 percent for other
members or R , as determined by the following equation:

R = 23 . 1(1 + D/L) (205-2)

where

A = area of floor or roof supported by the member, nr
D - dead load per square meter of area supported by the
member, kPa

L = unit live load per square meter of area supported by
the member, kPa
R ~ reduction in percentage,

r = rate of reduction equal to 0.08 for floors. See Table
205-3 for roofs

For storage loads exceeding 4.8 kPa, no reduction shall be
made, except that design live loads on columns may be
reduced 20 percent.

The live load reduction shall not exceed 40 percent in
garages for the storage of private pleasure cars having a
capacity of not more than nine passengers per vehicle.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-20 CHAPTER 2 - Minimum Design Loads

205*6 Alternate Floor Live Load Reduction

As an alternate to Equation 205-1, the unit live loads set
forth in Table 205-1 may be reduced in accordance with
Equation 205-3 on any member, including flat slabs,
having an influence area of 40 m 2 or more.

L = L o

0.25 + 4.57

/A,

(205-3)

where

A, = influence area, nr

L = reduced design live load per square meter of area
supported by the member

L 0 = unreduced design live load per square meter of area
supported by the member (Table 205-1)

The influence area A, is four times the tributary area for
a column, two times the tributary area for a beam, equal to
the panel area for a two-way slab, and equal to the product
of the span and the full flange width for a precast T-beam.

The reduced live load shall not be less than 50 percent of
the unit live load L 0 for members receiving load from one
level only, nor less than 40 percent of the unit live load L 0
for other members.

5. Greenhouses, lath houses
agricultural buildings. 5

1 For special-purpose roofs, see Section 205.4.4.

2 See Sections W5 5 and 205.6 for live-load reductions. The rate of reduction r in Equation
if, fall" The Lin, um reduction, II. shall no, exceed the value indicated m the table.

1 A flat roof is any roof with a slope less than 1 .unit vertical in 48-unit horizontal 1 2 % slope),
is in addition to the ponding load required by Section 206. 7.

4 See definition in Section 202 .

5 See Section 205.4.4 for concentrated load requirements for greenhouse roof members.

205-1 shall be as indicated
The live load for flat roofs

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-21

loads;;

20 6.1 General

In addition to the other design loads specified in this
chapter, structures shall be designed to resist the loads
specified in this section and the special loads set forth in
Table 205-2. See Section 207 for design wind loads and
Section 208 for design earthquake loads.

206.2 Other Loads

Buildings and other structures and portions thereof shall be
designed to resist all loads due to applicable fluid
pressures, f\ lateral soil pressures, H , ponding loads, P,
and self-straining forces, 7\ See Section 206.7 for ponding
loads for roofs.

206.3 Impact Loads

The live loads specified in Sections 205.3 shall be assumed
to include allowance for ordinary impact conditions.
Provisions shall be made in the structural design for uses
and loads that involve unusual vibration and impact forces.
See Section 206.9.3 for impact loads for cranes, and
Section 206, 10 for heliport and helistop landing areas.

206.3.1 Elevators

All elevator loads shall be increased by 100% for impact

206.3.2 Machinery

For the purpose of design, the weight of machinery and
moving loads shall be increased as follows to allow for
impact:

1 . Elevator machinery 1 00%

2. Light machinery, shaft- or motor-driven 20%

3. Reciprocating machinery or power-driven units 50%

4. Hangers for floors and balconies 33%

All percentages shall be increased where specified by the
manufacturer.

206.4 Anchorage of Concrete and Masonry Walls

Concrete and masonry walls shall be anchored as required
by Section 104.3.3. Such anchorage shall be capable of
resisting the load combinations of Section 203.3 or 203.4
using the greater of the wind or earthquake loads required
by this chapter or a minimum horizontal force of 4 kN/m
of wall, substituted for E.

206.5 Interior Wall Loads

Interior walls, permanent partitions and temporary
partitions that exceed 1.8 m in height shall be designed to
resist all loads to which they are subjected but not less than
a load, L, of 0.25 kPa applied perpendicular to the walls.
The 0.25 kPa load need not be applied simultaneously with
wind or seismic loads. The deflection of such walls under
a load of 0.25 kPa shall not exceed 1/240 of the span for
walls with brittle finishes and 1/120 of the span for walls
with flexible finishes. See Table 208-13 for earthquake
design requirements where such requirements are more
restrictive.

Exception:

Flexible, folding or portable partitions are not required to
meet the load and deflection criteria but must be anchored
to the supporting structure to meet the provisions of this
code .

206.6 Retaining Walls

Retaining walls shall be designed to resist loads due to the
lateral pressure of retained material in accordance with
accepted engineering practice. Walls retaining drained soil,
where the surface of the retained soil is level, shall be
designed for a load, H, equivalent to that exerted by a fluid
weighing not less than 4.7 kPa per meter of depth and
having a depth equal to that of the retained soil. Any
surcharge shall be in addition to the equivalent fluid
pressure.

Retaining walls shall be designed to resist sliding by at
least 1 .5 times the lateral force and overturning by at least
1.5 times the overturning moment, using allowable stress
design loads.

206.7 Water Accumulation

All roofs shall be designed with sufficient slope or camber
to ensure adequate drainage after the long-term deflection
from dead load or shall be designed to resist ponding load,
P, combined in accordance with Section 203.3 or 203.4.
Ponding load shall include water accumulation from any
source due to deflection.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-22 CHAPTER 2 - Minimum Design Loads

206.8 Uplift on Floors and Foundations

In the design of basement floors and similar approximately
horizontal elements below grade, the upward pressure of
water, where applicable, shall be taken as the full
hydrostatic pressure applied over the entire area. The
hydrostatic load shall be measured from the underside of
the construction. Any other upward loads shall be included
in the design.

Where expansive soils are present under foundations or
slabs-on-ground, the foundations, slabs, and other
components shall be designed to tolerate the movement or
resist the upward loads caused by the expansive soils, or
the expansive soil shall be removed or stabilized around
and beneath the structure.

206.9 Crane Loads

206.9.1 General

The crane load shall be the rated capacity of the crane.
Design loads for the runway beams, including connections
and support brackets of moving bridge cranes and monorail
cranes shall include the maximum wheel loads of the crane
and the vertical impact, lateral, and longitudinal forces
induced by the moving crane.

206.9.2 Maximum Wheel Load

The maximum wheel loads shall be the wheel loads
produced by the weight of the bridge, as applicable, plus
the sum of the rated capacity and the weight of the trolley
with the trolley positioned on its runway where the
resulting load effect is maximum.

206.9.3 Vertical Impact Force

The maximum wheel loads of the crane shall be increased
by the percentages shown below to determine the induced
vertical impact or vibration force:

Monorail cranes (powered)

25%

Cab-operated or remotely operated bridge

cranes (powered)

25%

Pendant-operated bridge cranes (powered)

10%

Bridge cranes or monorail cranes with

hand-geared ridge, trolley and hoist

206.9.4 Lateral Force

The lateral force on crane runway beams with electrically jj
powered trolleys shall be calculated as 20% of the sum of
the rated capacity of the crane and the weight of the hoist
and trolley. The lateral force shall be assumed to act
horizontally at the traction surface of a runway beam, in
either direction perpendicular to the beam, and shall be |j
distributed with due regard to the lateral stiffness of the
runway beam and supporting structure.

i M
:

206.9.5 Longitudinal Forces

The longitudinal force on crane runway beams, except fori
bridge cranes with hand-geared bridges, shall be calculated
as 10% of the maximum wheel loads of the crane. The
longitudinal force shall be assumed to act horizontally at
the traction surface of a runway beam, in either direction
parallel to the beam.

206.10 Heliport and Helistop Landing Areas

In addition to other design requirements of this chapter^
heliport and helistop landing or touchdown areas shall be :
designed for the following loads, combined in accordance
with Section 203.3 or 203.4:

1 . Dead load plus actual weight of the helicopter.

2. Dead load plus a single concentrated impact load, Ljl
covering 0. 1 0 nr of 0.75 times the fully loaded weight
of the helicopter if it is equipped with hydraulic-type
shock absorbers, or 1.5 times the fully loaded weighty
of the helicopter if it is equipped with a rigid or skid'
type landing gear.

The dead load plus a uniform live load, L, of 4.8 kPa. The
required live load may be reduced in accordance with
Section 205.5 or 205.6.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-23

^Buildings and other vertical structures shall be designed
and constructed to resist wind loads as specified and
presented in Sections 207A through 207F.

0 Antenna towers and antenna supporting structures shall be
; designed and constructed to resist wind loads as specified
'and presented in ANSI/TIA-222-G-2005, entitled as
“Structural Standards for Steel Antenna Towers and
Antenna Supporting Structures and ANSI/TIA-222-G-1-
2007, entitled as 44 Structural Standards for Steel Antenna
Towers and Antenna Supporting Structures - Addendum L

§207A General Requirements

in this

code have been significantly revised from NSCP 2001 and
NSCP 2010 editions: The goal was to improve the
Organization, clarity, and use of the wind load provisions
by creating individual sub-sections organized according to
applicable major subject areas: The wind load
provisions are now presented in Sections 207 A through
207F as opposed to prior editions ; where the provisions
were contained in a single section.

Sec turn 207 A provides the basic wind design
parameters that are applicable to the various wind

2078 through 207F . Items covered in Section 207 A
include definitions, basic wind speed, exposure
categories, internal ■ pressures, Cw enclosure
classification, gust-effects, and topographic factors,
among others! A general description of each section is
provided below: C

a Section 207 B discusses about Directional Procedure
for Enclosed, Partially Enclosed, and Open Buildings
of All Heights: The procedure is the former “ buildings
of all heights method ” in NSCP 2010 (ASCE 7-05),
Method 2 A simplified procedure, based on the
Directional Procedure, is provided for buildings up to
48m in heigltUrA\g :v/v. : :vev;w

3 Section 207C discusses about Envelope Procedure for

Enclosed and Partially Enclosed Low-Rise Buildings:
This procedure is the former “low-rise buildings
method" in NSCP 2010 (ASCE 7-05) Method 2. This
section also incorporates NSCP 2010 (ASCE 7-05)
Method I for MWFRS applicable to the MWFRS of

enclosed simple diaphragm buildings less than 18 m
in height .

a Section 207 D discusses Other Structures and Building

Appurtenances: A single section is dedicated to
determining wind loads on non-building structures
such as signs, rooftop structures, and towers, wA

“ Section 207 E discusses about Components and
Cladding . This code addresses the determination of
component and cladding loads in a single section
Analytical and simplified methods are provided based
on the building height. Provisions for open buildings
and building appurtenances are also addressed.

a Section 207 F discusses about Wind Tunnel Procedure .

207A.1 Procedures
207A.1.1 Scope

Buildings and other structures, including the Main Wind-
Force Resisting System (MWFRS) and all components and
cladding (C&C) thereof, shall be designed and constructed
to resist the wind loads determined in accordance with
Section 207A through 207F. The provisions of this section
define basic wind parameters for use with other provisions
contained in this code.

Commentary:

The procedures specified in this code provide wind
pressures and forces for the design of MWFRS and for the
design of components and cladding (C&C) of buildings
and other structures. The procedures involve the
determination of wind directionality and velocity pressure,
the selection or determination of an appropriate gust effect
factor, and the selection of appropriate pressure or force
coefficients. The procedure allows for the level of
structural reliability required, the effects of differing wind
exposures, the speed-up effects of certain topographic
features such as hills and escarpments, and the size and
geometiy of the building or other structure under
consideration. The procedure differentiates between rigid
and flexible biuldings and other structures, and the results
generally envelop the most critical load conditions for the
design of MWFRS as well as C&C.

The pressure and force coefficients provided in Sections
207B , 207 C, 207 D, and 207E have been assembled from
the latest boundary-layer wind-tunnel and full-scale tests
and from previously available literature. Because the
boundary-layer wind-tunnel results were obtained for
specific types of building, such as low - or high-rise
buildings and buildings having specific types of structural

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-24 CHAPTER 2 - Minimum Design Loads

framing systems, the designer is cautioned against
indiscriminate interchange of values among the figures
and tables.

207A.1.2 Permitted Procedures

The design wind loads for buildings and other structures,
including the MWFRS and C&C elements thereof, shall be
determined using one of the procedures as specified in this
article. An outline of the overall process for the
determination of the wind loads, including section
references, is provided in Figure 207A.1-L

Commentary:

The design wind loads for buildings and other
structures , including the MWFRS and C&C elements
thereof shall be determined using one of the procedures
as specified in this article . An outline of the overall
process for the determination of the wind loads,
including section references, is provided in Figure
207 A. 1-1.

This version of the wind load standard provides several
procedures (as illustrated in Table 207 A. 1-1) from
which the designer can choose.

For MWFRS:

1. Directional Procedure for Buildings of All Heights
(Section 207B)

2. Envelope Procedure for Low-Rise Buildings
(Section 207C)

3. Directional Procedure for Building Appurtenances
and Other Structures (Section 207D)

4. Wind Tunnel Procedure for All Buildings and Other
Structures (Section 207 F)

For Components and Cladding:

1. Analytical Procedure for Buildings and Building
Appurtenances (Section 207E)

2. Wind Tunnel Procedure for All Buildings and Other
Structures (Section 207 F)

A M simplified method’* for which the designer can select
wind pressures directly from a table without any
calculation ; when the building meets all the
requirements for application of the method, is provided
for designing buildings using the Directional Procedure
(Section 207 B, Part 2), the Envelope Procedure (Section

207C, Part 2) and the Analytical Procedure jorffi
Components and Cladding (Section 207E).

Limitations . The provisions given under Section ||
207 A. 1.2 apply to the majority of site locations and
buildings and structures , but for some projects, these
provisions may be inadequate. Examples of site H
locations and buildings and structures (or portions f
thereof) that may require other approved standards, f
special studies using applicable recognized literature f
pertaining to wind effects , or using the wind tunnel |g
procedure of Section 207 F include:

1. Site locations that have channeling effects or wakes
from upwind obstructions. Channeling effects cant,
be caused by topographic features (e.g., a mountain §
gorge) or buildings (e.g., a neighboring tall
building or a cluster of tall buildings). Wakes cant |'
be caused by hills or by buildings or other f
structures. S

2. Buildings with unusual or irregular geometric
shape, including barrel vaults, and other buildings
whose shape (in plan or vertical cross-section)
differs significantly from the shapes in Figures %
207B.4-1, 207 B. 4-2, 207 B. 4-7, 207 C. 4-1, anc§ :
207E.4-1 to 207E.4-7. Unusual or irregular f
geometric shapes include buildings with multiple |
setbacks, curved facades, or irregular plansi
resulting from significant indentations org
projections, openings through the building, org
multi-tower buildings connected by bridges.

3. Buildings with response characteristics that result
in substantial vortex-induced and/or torsional
dynamic effects, or dynamic effects resulting from I
aero-elastic instabilities such as flutter or |
galloping. Such dynamic effects are difficult to')
anticipate, being dependent on many factors, but)
should be considered when any one or more of the
following apply:

ii.

in.

iv.

The height of the building is over 120 m. ]\

The height of the building is greater than 4
times its minimum effective width B min . as
defined below. 1

The lowest natural frequency of the building
is less than n t = 0.25 Hz.

The reduced velocity

niBv

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-25

:Wiere-\:

-f,- z “ 0 . 6 h

V z " the mean hourly velocity at height z

The minimum effective width B min is defined as the
minimum value of £ hiBfY, h t considering all wind
directions . The summations are performed over the
|| %eight of the building for each wind direction, h it is the
height above grade of level /, and B L is the width at level
' i normal to the wind direction.

4 \ Bridges, cranes , electrical transmission lines,
guyed masts , highway signs and lighting structures ,
telecommunication towers, and flagpoles.

:[ When undertaking detailed studies of the dynamic
response to wind forces, the fundamental frequencies of
: f$he structure in each direction under consideration
should be established using the structural properties
ami deformational characteristics of the resisting
, elements in a properly substantiated analysis, and not
utilizing approximate equations based on height f

Shielding * Due to the lack of reliable analytical
% procedures for predicting the effects of shielding
f provided by buildings and other structures or by
f topographic features, reductions in velocity pressure
%fhte to shielding are not permitted under the provisions
fpf this chapter. However, this does not preclude the
i determination of shielding effects and the corresponding
Inductions in velocity pressure by means of the wind
fhmnel procedure in Section 207F .

207AJ.2.1 Main Wind-Force Resisting System
(MWFRS)

V\ tnd loads for MWFRS shall be determined using one of
||Iie fallowing procedures:

1. Directional Procedure for buildings of all heights as
specified in Section 207B for buildings meeting the
requirements specified therein;

2. Envelope Procedure for low-rise buildings as specified
in Section 207C for buildings meeting the
requirements specified therein;

3* Directional Procedure for Building Appurtenances
(rooftop structures and rooftop equipment) and Other
Structures (such as solid freestanding walls and solid
j| :/ freestanding signs, chimneys, tanks, open signs, lattice
frameworks, and trussed towers) as specified in
Section207D; or

4. Wind Tunnel Procedure for all buildings and all other
structures as specified in Section 207F.

207A.L2.2 Components and Cladding

Wind loads on components and cladding on all buildings
and other structures shall be designed using one of the
following procedures:

1 . Analytical Procedures provided in Parts 1 through 6,
as appropriate, of Section 207E; or

2. Wind Tunnel Procedure as specified in Section 207F.

207A.2 Definitions

The following definitions apply to the provisions of
Section 207:

APPROVED is an acceptable to the authority having
jurisdiction.

BASIC WIND SPEED, V is a three-second gust speed at
10m above the ground in Exposure C (see Section
207A.7.3) as determined in accordance with Section
207A.5.1.

BUILDING, ENCLOSED is a building that does not
comply with the requirements for open or partially
enclosed buildings.

BUILDING ENVELOPE is a cladding, roofing, exterior
walls, glazing, door assemblies, window assemblies,
skylight assemblies, and other components enclosing the
building.

BUILDING AND OTHER STRUCTURE, FLEXIBLE
are slender buildings and other structures that have a
fundamental natural frequency less than 1 Hz.

BUILDING, LOW-RISE are enclosed or partially
enclosed buildings that comply with the following
conditions:

1 . Mean roof height h less than or equal to 1 8m.

2. Mean roof height h does not exceed least horizontal
dimension.

BUILDING, OPEN is a building having each wall at least
80 percent open. This condition is expressed for each wall
by the equation A 0 > 0. 8A g .

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-26 CHAPTER 2 - Minimum Design Loads

A g = the gross area of that wail in which A 0 is
identified, in m 2

A 0 = total area of openings in a wall that receives
positive external pressure, in m 2

Figure 207 A. 1-1

Outline of Process for Determining Wind Loads. Additional Outlines and User Notes are Provided at the Beginning of each
Chapter for more Detailed Step-By-Step Procedures for Determining the Wind Loads

These conditions are expressed by the following equations:

1. A a > 1. 10A„i

2. A 0 > 0.37 m 2 or 0.0L4 g , whichever is smaller, and
A oi /A si < 0.20

where:

A 0 ,Ag = are as defined for Open Building
A oi = the sum of the areas of openings in the
building envelope (walls and roof) not
including A 0 , in m 2

A si = the sum of the gross surface areas of the
building envelope (walls and roof) not
including A g , in m 2

Association of Structural Engineers of the Philippines, Inc. (ASEP)

BUILDING, PARTIALLY ENCLOSED is a building
that complies with both of the following conditions:

1. The total area of openings in a wall that receives
positive external pressure exceeds the sum of the areas
of openings in the balance of the building envelope
(walls and roof) by more than 10 percent.

2. The total area of openings in a wall that receives
positive external pressure exceeds 0.37 nr.

or 1 percent of the area of that wall, whichever is smaller,
and the percentage of openings in the balance of the
building envelope does not exceed 20 percent.

Components can be part of the MWFRS when they act as
or roof diaphragms, but they may also be
individual components. The engineer needs to
^^Ullpriate loadings for design of components, which
certain components to be designed for more
llhfeohe type of loading, for example, long-span roof
p^^^P||||Id^ be designed for loads associated with
'MWFRS* and individual members of trusses should also be
^ils%h ; ed for component and cladding loads ( Mehta and
Examples of cladding include wall
curtain walls, roof coverings, exterior windows
operable) and doors, and overhead doors.

ft ^^PHRAGM in wind load applications has been added
7-10. This definition, for the case of untopped

^^gdecks, differs somewhat from the definition used in
of ASCE 7-10 because diaphragms under
^^J^Bads':are expected to remain essentially elastic.

WIND AREA, A is an effective wind area
^|||h| area of the building surface used to determine ( GC p ).
^^p||%eadoes not necessarily correspond to the area of the
^^^ffinf-surface contributing to the force being considered.

cases arise. In the usual case, the effective wind area
correspond to the area tributary to the force
^fc^fipbnent being considered. For example, for a cladding

the effective wind area may be equal to the total area
h6 panel; For a cladding fastener, the effective wind
the area of cladding secured by a single fastener. A
^H^^liidnimay receive wind from several cladding panels. In
^^tcase, the effective wind area is the area associated with
P^|^^t|i<ddbad that is transferred to the mullion.

^^^^^||cond case arises where components such as roofing
wall studs, or roof trusses are spaced closely
The area served by the component may become
anc * narrow - To better approximate the actual load
distribution in such cases, the width of the effective wind
|0g|^uscd t0 eva ^ uate (fiCp) need not be taken as less than
”^^^^|| : hird the length of the area. This increase in effective
y y- Wind area has the effect of reducing the average wind
pressure acting on the component. Note, however, that this
e wind area should only be used in determining the
^^CC p ) in Figures 207E.4-1 through 207E.4-6 and 207E.4-
^^^||||||edndiiced wind load should be applied over the actual
tributary to the component being considered.

^^^^imembrane roof systems, the effective wind area is the
, ■ : aiea of an insulation board (or deck panel if insulation is
|/|pTft ot use d) if the boards are fully adhered (or the membrane
|l a bhered directly to the deck). If the insulation boards or
^^|!|||mbrane are mechanically attached or partially adhered,
e — c ^ ve w * n ^ area Is the area of the board or membrane
secured by a single fastener or individual spot or row of
fjiflg adhesive.

CHAPTER 2 - Minimum Design Loads 2-29

For typical door and window systems supported on three
or more sides, the effective wind area is the area of the door
or window under consideration. For simple spanning doors
(e.g., horizontal spanning section doors or coiling doors),
large specialty constructed doors (e.g., aircraft hangar
doors), and specialty constructed glazing systems, the
effective wind area of each structural component
composing the door or window system should be used in
calculating the design wind pressure.

MAIN WIND-FORCE RESISTING SYSTEM
(MWFRS) can consist of a structural frame or an
assemblage of structural elements that work together to
transfer wind loads acting on the entire structure to the
ground. Structural elements such as cross-bracing, shear
walls, roof trusses, and roof diaphragms are part of the
Main Wind-Force Resisting System (MWFRS) when they
assist in transferring overall loads (Mehta and Marshall
1998).

WIND-BORNE DEBRIS REGIONS are defined to alert
the designer to areas requiring consideration of missile
impact design. These areas are located within tropical
cyclone prone regions where there is a high risk of glazing
failure due to the impact of wind-borne debris.

207A.3 Symbols and Notations

The following symbols and notation apply only to the
provisions of Section 207A through 207F:

A = effective wind area, in m 2

Af - area of open buildings and other

structures either normal to the wind
direction or projected on a plane
normal to the wind direction, in m 2

A s = the gross area of that wall in which A 0
is identified, in m 2

Agi = the sum of the gross surface areas of
the building envelope (walls and roof)
not including A g , in m 2

A 0 - total area of openings in a wall that
receives positive external pressure, in
m 2

A oi = the sum of the areas of openings in the
building envelope (walls and roof) not
including A 07 in m 2

A og ~ total area of openings in the building
envelope in m 2

A s = gross area of the solid freestanding
wall or solid sign, in m 2

a = width of pressure coefficient zone, in
m

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-30 CHAPTER 2 - Minimum Design Loads

C N

(GC r )

(GC P )

i GC Pf)

(GCpt)

(GC pn )
Sq
g R

- horizontal dimension of building
measured normal to wind direction, in
m

- mean hourly wind speed factor in
Equation 207A.9-16 from Table
207A.9-1

= 3-s gust speed factor from Table

207A.9-1

= force coefficient to be used in
determination of wind loads for other
structures

= net pressure coefficient to be used in
determination of wind loads for open
buildings

= external pressure coefficient to be
used in determination of wind loads
for buildings

= turbulence intensity factor in
Equation 207A.9-7 from Table
207A.9-1

- diameter of a circular structure or
member, in m

- depth of protruding elements such as
ribs and spoilers, in m

- design wind force for other structures,
in N

= gust-effect factor

= gust-effect factor for MWFRS of
flexible buildings and other structures

- product of external pressure
coefficient and gust-effect factor to be
used in determination of wind loads
for rooftop structures

= product of external pressure
coefficient and gust-effect factor to be
used in determination of wind loads
for buildings

- product of the equivalent external
pressure coefficient and gust-effect
factor to be used in determination of
wind loads for MWFRS of low-rise
buildings

- product of internal pressure
coefficient and gust-effect factor to be
used in determination of wind loads
for buildings

= combined net pressure coefficient for
a parapet

= peak factor for background response
in Equations 207A.9-6 and 207 A. 9-1 0

= peak factor for resonant response in
Equation 207A.9-10

= peak factor for wind response in
Equations 207A.9-6 and 207A.9-10

- height of hill or escarpment in
Figure 207A.8-1, in m

h = mean roof height of a building or
height of other structure, except that
eave height shall be used for roof |jj
angle 6 less than or equal to 10°, in m

h e = roof eave height at a particular wail, or 1

the average height if the eave varies
along the wall

h p = height to top of parapet in Figure
207B.6-4 and 207E.7-1

I z ~ intensity of turbulence from

Equation 207A.9-7

K 1 ,K 2 ,I <3 “ multipliers in Figure 207A.8-1 to
obtain K zt

K d = wind directionality factor in |

Table 207A.6-1

K h = velocity pressure exposure coefficient
evaluated at height z = h

K 2 - velocity pressure exposure coefficient
evaluated at height z

K zt “ topographic factor as defined in

Section 207A.8 j

L - horizontal dimension of a building

measured parallel to the wind
direction, in m

L h = distance upwind of crest of hill or |jj
escarpment in Figure 207A.8-1 to . J
where the difference in ground |j

elevation is half the height of the hill
or escarpment, in m

L r = horizontal dimension of return comer |
for a solid freestanding wall or solid
sign from Figure 207D.4-1, in m

L 7 ~ integral length scale of turbulence, in

PnetlO

integral length scale factor from |
Table 207A.9-l,m

reduced frequency from |

Equation 207A.9-14

approximate lower bound natural ^
frequency (Hz) from Section
207A.9.2

fundamental natural frequency, Hz 1
design pressure to be used iri|jj|
determination of wind loads for
buildings, in N/m 2

wind pressure acting on leeward & ce jM

in Figure 207B.4-8, in N/m 2

net design wind pressure from |

Equation 207E.5-1, in N/m 2

net design wind pressure for Exposure j

B at h = 10 m and / = 1.0 from

Figure 207E.5-1, in N/m 2

combined net pressure on a parapet

from Equation 207B.4-5, in N/m 2

net design wind pressure front

Equation 207C.6-1, in N/m 2

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-31

simplified design wind pressure for
Exposure B at h — 10 m and
/ s= 1.0 from Figure 207C.6-1, in
N/nf

wind pressure acting on windward
face in Figure 207B.4-8, in N/m 2
background response factor from
Equation 207A.9-8
velocity pressure, in N/m 2
velocity pressure evaluated at height
z = ft, in N/m 2

velocity pressure for internal pressure
determination, in N/m 2
velocity pressure at top of parapet, in
N/nr

velocity pressure evaluated at height z
above ground, in N/m 2
resonant response factor from
Equation 207A.9-12
values from Equations 207A.9-15
reduction factor from

Equation 207A.1 1-1
value from Equation 207A.9-13
vertical dimension of the solid
freestanding wall or solid sign from
Figure 207D.4-1, in m
rise-to-span ratio for arched roofs
height-to-width ratio for solid sign
basic wind speed obtained from
Figure 207A.5-1A through 207 A. 5-
1C, in m/s. The basic wind speed
corresponds to a 3-s gust speed at 10
m above the ground in Exposure
Category C

unpartitioned internal volume, m 3
mean hourly wind speed at height z
m/s

width of building in Figures 207E.4-3
and 207E.4-5A and 207E.4-5B and
width of span in Figures 207E.4-4 and
207E.4-6, in m

distance upwind or downwind of crest
in Figure 207A.8-1, in m
height above ground level, in m
equivalent height of structure, in m
nominal height of the atmospheric
boundary layer used in this code.
Values appear in Table 207A.9-1
exposure constant from Table
207A.9-1

€

- damping ratio, percent critical for

buildings or other structures
= ratio of solid area to gross area for
solid freestanding wall, solid sign,
open sign, face of a trussed tower, or
lattice structure

= integral length scale power law
exponent in Equation 2 07 A. 9-9 from
Table 207A.9-1

= adjustment factor for building height
and exposure from Figures. 207C.6-1
and 207 E. 5-1

= value used in Equation 207A.9-15
(see Section 207A.9.4)

= angle of plane of roof from horizontal,
in degrees

207A.4 General
207A.4.1 Sign Convention

Positive pressure acts toward the surface and negative
pressure acts away from the surface.

207AA2 Critical Load Condition

Values of external and internal pressures shall be combined
algebraically to determine the most critical load.

207AA3 Wind Pressures Acting on Opposite Faces of
Each Building Surface

In the calculation of design wind loads for the M WFRS and
for components and cladding for buildings, the algebraic
sum of the pressures acting on opposite faces of each
building surface shall be taken into account.

Commentary:

Section 207A.4.3 is included in the code to ensure that
internal and external pressures acting on a building
surface are taken into account by determining a net
pressure from the algebraic sum of those pressures . For
additional information on the application of the net
components and cladding wind pressure acting across a
multilayered building envelope system, including
air-permeable cladding , refer to Section C207E . 1.5.

3-s gust-speed power law exponent
from Table 207A.9-1
reciprocal of a from Table 207A.9-1
mean hourly wind-speed power law
exponent in Equation 207A.9-16 from
Table 207A.9-1

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-32 CHAPTER 2 - Minimum Design Loads

207A.5 Wind Hazard Map
207A.5.1 Basic Wind Speed

The basic wind speed, V, used in the determination of
design wind loads on buildings and other structures shall
be determined from Figure 207A.5-1 as follows, except as
provided in Section 207A.5.2 and 207 A. 5.3:

For Occupancy Category III, IV and V buildings and other
structures - use Figure 207A.5-1 A.

For Occupancy Category 11 buildings and other structures

- use Figure 207A.5-1.B.

For Occupancy Category I buildings and other structures

- use Figure 207A.5-1C.

The wind shall be assumed to come from any horizontal
direction. The basic wind speed shall be increased where
records or experience indicate that the wind speeds are
higher than those reflected in Figure 207A.5-1 .

Commentary:

This edition of NSCP departs from prior editions by
providing wind maps that are directly applicable for
determining pressures for strength design approaches .
Rather than using a single map with importance factors
and a load factor for each building occupancy category,
in this edition there are different maps for different
categories of building occupancies . The updated maps
are based on a new and more complete analysis of
tropical cyclone characteristics (Vickery et al 2008a,
2008b and 2009) performed over the past 10 years.

The decision to move to multiple-strength design maps
in conjunction with a wind load factor of LO instead of
using a single map used with an importance and a load
factor of 1.6 relied on several factors important to an
accurate wind specification :

1. A strength design wind speed map brings the wind
loading approach in line with that used for seismic
loads in that they both essentially eliminate the use

of a load factor for strength design.

2. Multiple maps remove inconsistencies in the use of
importance factors that actually should vary with ?|f
location and between tropical cyclone-prone and
non-tropical cyclone-prone regions for Occupcmcyf)
Category ill, IV and V structures and acknowledge^
that the demarcation between tropical cyclone anclfj
non-tropical cyclone winds change with the
recurrence interval.

3 .

The new maps establish uniformity in the return
period for the design-basis winds , and they more j
clearly convey that information.

The new maps, by providing the design wind speed
directly , more clearly inform owners and their : ||
consultants about the storm intensities for which y
designs are performed.

Selection of Return Periods, in the development oftheyy
design wind speed map used in Section 207 NSCP 2010, yy
the Wind Load Subcommittee evaluated the wind'f
importance factor , I w , that had been in use since 1982.%
The task committee recognized that using a uniform
value of the wind importance factor probably was not
appropriate because risk varies with location along the y
coast.

To determine the return periods to be used in the newj
mapping approach, the task committee needed to meet y
with PAG AS A scientists, gather historical records and
evaluate representative return periods for wind speeds |
determined in accordance with Section 207 NSCP 2010
and earlier, wherein determination of pressures \
appropriate for strength design started with mapped
wind speeds, but involved multiplication by importance's
factors and a wind load factor to achieve pressures that |
were appropriate for strength design. Furthermore , it -
was assumed that the variability of the wind speed
dominates the calculation of the wind toad factor. The
strength design wind load, W T . is given as:

w T = C f (V S0 I) 1 2 W lf

(C207A.5-1)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-33

s©

® 1.4

■H , _

> 1.3

— DURST

GUST DURATION, sec

Figure C207A.5-!

Maximum Speed Averaged over t s to Hourly Mean Speed

P where C f is a building, component, or structure specific
coefficient that includes the effects of things like
building height , building geometry, terrain , and gust
ifactor as computed using the procedures outlined in
0fj$CP 2010. F 50 is the 50-year return period design
iywind speed. W LF is the wind load factor, and / is the
^importance factor.

Starting with the nominal return period of 50 years, the
% yatio of the wind speed for any return period to the 50-
ifear return period wind speed can he computed from
fPeterka and Shahid (1998):

% v t/V$o = [0.36 + 0. lln(127)]

(C207A.5-2)

( where T is the return period in years and V T is the T-
year return period wind speed. The strength design wind
c load ' W T , occurs when:

C F Vlo W LF

(C207A.5-3)

p V t /V 50 = [0. 36 4- 0. ll?i(127)] (C2Q7A.5-4)

H =4wZ

and from Equation C207A.5-4, the return period T

7 = 0. 00228 exp(l0jWw) (C207A.5-5)

Using the wind load factor of 1.6 as specified in Section
207 NSCP 2010, from Equation C207A.5-5 we get
T ” 709 years; and therefore V design ~ ^709/V^F **
^700 Thus for Occupancy Category IV

structures , the basic wind speed is associated with a
return period of 700 years, or an annual exceedance
probability of 0.0014.

The importance factor used in Section 207 NSCP 2010
and earlier for the computation of wind loads for the
design of Occupancy Category I and 11 structures is
defined so that the nominal 50-year return period non-
tropical cyclone wind speed is increased to be
representative of a 100-year return period value.
Following the approach used above to estimate the
resulting effective strength design return period
associated with a 50-year basic design speed, in the case
of the 100-year return period basic wind speed in the
non-tropical cyclone-prone regions, we find that:

T = 00228 exp[lO(K 100 /K 50 )7i4^] (C207A.5-6)

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-34 CHAPTER 2 - Minimum Design Loads

whereforViQo/Vso computed from Equation C207A.5-
4 with W if = L6, we find T = 1,697 years. In the
development of Equation C 7 07 A, 5 -6, the term
(V 10 Q /V 50 )W if replaces the W LF used in
Equation €207 A. 5-5, effectively resulting in a higher
load factor for Occupancy Category 1, 11 and III
structures equal to ^lfO^ioo/Pso) 2 * Thus for
Occupancy Category I and II structures, the basic wind
speed is associated with a return period of 1 , 700 years,
or an annual exceedance probability of 0,000588,
Similarly, the 25-year return period wind speed
associated with Occupancy Category III, IV and V
buildings equates to a 300-year return period wind
speed with a wind load factor of LO.

Wind Speeds . The wind speed maps of Figure 207 A. 5-1
present basic wind speeds for the entire archipelago of
the Philippines . The wind speeds correspond to 3 -sec
gust speeds at 10 m above ground for exposure category

Serviceability Wind Speeds . For applications of
serviceability, design using maximum likely events, or
other applications, it may be desired to use wind speeds
associated with mean recurrence intervals other than
those given in Figures 207A.5-1A to 207 A, 5- 1C, To
accomplish this, previous editions of NSCP 2010
provided tables with factors that enabled the user to
adjust the basic design wind speed (previously having a
return period of 50 years to wind speeds associated with
other return periods.

For applications of serviceability, design using
maximum likely events, or other applications, Appendix
C presents maps of peak gust wind speeds at 10 m above
ground in Exposure C conditions for return periods of
10, 25, 50, and 100 years.

The probability P n that the wind speed associated with
a certain annual probability P a will he equaled or
exceeded at least once during an exposure period of n
years is given by:

P n - 1 - (1 - Pa) 71 (C207A.5-7)

As an example, if a wind speed is based upon P a ~ 0.02
(50 -year mean recurrence interval), there exists a
probability of 0.40 that this speed will be equaled or
exceeded during a 25-year period \ and a 0.64
probability of being equaled or exceeded in a 50-year
period.

Similarly, if a wind speed is based upon P a - 0.00143
(700-year mean recurrence interval), there exists a
3.5% probability that this speed will be equaled or
exceeded during a 25-year period, and a 6.9% i |
probability > of being equaled or exceeded in a 50-year
period.

Some products have been evaluated and test methods
have been developed based on design wind speeds that
are consistent with the unfactored load effects typically
used in Allowable Stress Design. Table C207A.5-6
provides conversion from the strength design-based
design wind speeds used in the ASCE 7-10 design wind
speed maps and the Section 207 NSCP 2010 design wind
speeds used in these product evaluation reports and test
methods. A column of values is also provided to allow
coordination with ASCE 7-93 design wind speeds.

207A.5.2 Special Wind Regions

Mountainous terrain, gorges, and special wind regions
shown in Figure 207A.5-1 shall be examined for unusual
wind conditions. The authority having jurisdiction shall, if
necessary, adjust the values given in Figure 207A.5-1 to
account for higher local wind speeds. Such adjustment!
shall be based on meteorological information and an
estimate of the basic wind speed obtained in accordance
with the provisions of Section 207A.5.3.

Commentary:

Although the wind speed map of Figure 207 A. 5- 1 is valid
for most regions of the country, there are special regions: )
in which wind speed anomalies are known to exist. Some off
these special regions are noted in Figure 207A.5-1. Winds
blowing over mountain ranges or through gorges or riven
valleys in these special regions can develop speeds that are :
substantially higher than the values indicated on the map.
When selecting basic wind speeds in these special regions f
use of regional climatic data and consultation with a wind
engineer or meteorologist is advised.

It is also possible that anomalies in wind speeds exist on a
micrometeorological scale. For example , wind speed-up
over hills and escarpments is addressed iff
Section 207 A. 8 . Wind speeds over complex terrain may bff
better determined by wind-tunnel studies as described in
Section 207 F. Adjustments of wind speeds should be made
at the micrometeorological scale on the basis of wind-
engineering or meteorological advice and used In
accordance with the provisions of Section 207A.5.3 when:
such adjustments are warranted. Due to the complexity of \
mountainous terrain and valley gorges in Hawaii , there \
are topographic wind speed-up effects that cannot bff

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-35

solely by Figure 207A.S-1 (Applied Research
PS2001).

2074.5.3 Estimation of Basic Wind Speeds from
Regional Climatic Data

|| area $ outside tropical cyclone-prone regions, regional
Wmmtic data shall only be used in lieu of the basic wind
itlpeeds given in Figure 207A.5-1 when (1) approved
Klxtreme-value statistical-analysis procedures have been
llmployed in reducing the data; and (2) the length of record,
Sampling error, averaging time, anemometer height, data
iffflity, and terrain exposure of the anemometer have been
Sfaken into account. Reduction in basic wind speed below
IlSMtof Figure 207A.5-1 shall be permitted.

I Jo tropical cyclone-prone regions, wind speeds derived
S^fSrbm simulation techniques shall only be used in lieu of the
§g||j$ib wind speeds given in Figure 207A.5-1 when
llpproved simulation and extreme value statistical analysis
procedures are used.

| In areas outside tropical cyclone-prone regions, when the
ftSasic wind speed is estimated from regional climatic data,
fJtHe basic wind speed shall not be less than the wind speed
ll&sociated with the specified mean recurrence interval, and
||he estimate shall be adjusted for equivalence to a 3-s gust
Hiind speed at 10m above ground in Exposure C. The data
f analysis shall be performed in accordance with this section.

using regional climatic data in accordance with the
of Section 207 A. 5. 3 and in lieu of the basic wind
given in Figure 207A.5-1, the user is cautioned that
1st factors, velocity pressure exposure coefficients ,
'i^Mifeffect factors , pressure coefficients , and force
f^^teients of this code are intended for use with the 3-s
;^^faspeed at 10m above ground in open counify . It is
necessary, therefore , that regional climatic data based on
| ^^^rent averaging time, for example, hourly mean or
fastest mile , he adjusted to reflect peak gust speeds at 10m
ground in open country. ,-fx.

■.ffjming local data, it should be emphasized that sampling
Fad to large uncertainties in specification of the
jWifdspeed. Sampling errors are the errors associated with
the limited size of the climatological data samples (years
Igf^cord^ of annual extremes). It is possible to have a
A P////V error in wind speed at an individual station with a
record length of 30 years. While local records of limited
extent of ten must be used to define wind speeds in special
wind areas, care and conservatism should be exercised in
Im^ir'use.

If meteorological data are used to justify a wind speed
lower than 1 77-hn/h 700-yr peak gust at 10 m , an' analysis
of sampling error is required to demonstrate that the wind
record could not occur by chance . This can - be
accomplished by showing that the difference between
predicted speed and 177 km/h contains two to three
standard deviations of sampling error (Simiu and Scanlan
1996). Other equivalent methods may be used.

207A.5.4 Limitation

Tornadoes have not been considered in developing the
basic wind-speed distributions.

207 A.6 Wind Directionality

The wind directionality factor, K d , shall be determined
from Table 207A.6-L This directionality factor shall only
be included in determining wind loads when the load
combinations specified in Sections 2.3 and 2.4 are used for
the design. The effect of wind directionality in determining
wind loads in accordance with Section 207F shall be based
on an analysis for wind speeds that conforms to the
requirements of Section 207A.5.3.

Commentary:

The wind load factor 1.3 in ASCE 7-95 included a ‘‘wind
directionality factor” of 0.85 (Ellingwood 1981 and
Ellingwood et at 1982). This factor accounts for two
effects: (1) The reduced probability of maximum winds
coming from any given direction and (2) the reduced
probability of the maximum pressure coefficient occurring
for any given wind direction . The wind directionality factor
(identified as K d in the code) is tabulated in Table 207A.6-
1 for different structure types. As new research becomes
available t this factor can be directly modified. Values for
the factor were established from references in the literature
and collective committee judgment. The K d value for round
chimneys , tanks, and similar structures is given as 0 95 in
recognition of the fact that the wind load resistance may
not be exactly the same in all directions as implied by a
value of 1. 0. A value of 085 might be more appropriate if
a triangular trussed frame is shrouded in a round cover. A
value of 1.0 might be more appropriate for a round
chimney having a lateral load resistance equal in all
directions. The designer is cautioned by the footnote to
Table 207 A. 6-1 and the statement in Section 207 A. 6, where
reference is made to the fact that this factor is only to be
used in conjunction with the load combinations specified
in Sectiom2ffdnd2ff^ASCE7i6;jff

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-36 CHAPTER 2 - Minimum Design Loads

207A.7 Exposure

For each wind direction considered, the upwind exposure
shall be based on ground surface roughness that is
determined from natural topography, vegetation, and
constructed facilities.

Commentary:

The descriptions of the surface roughness categories
and exposure categories in Section 207 A. 7 have been
expressed as far as possible in easily understood verbal
terms that are sufficiently precise for most practical
applications. Upwind surface roughness conditions
required for Exposures B and D are shown
schematically in Figures C207A.7-1 and C207A.7-2,
respectively . For cases where the designer wishes to
make a more detailed assessment of the surface
roughness category and exposure category , the
following more mathematical description is offered for
guidance (Irwin 2006). The ground surface roughness is
\ best measured in terms of a roughness length parameter
called z 0 . Each of the surface roughness categories B
through D correspond to a range of values of this
parameter, as does the even rougher category A used in
previous versions of the code in heavily built-up urban
areas but removed in the present edition . The range of
z 0 in meters (m) for each terrain category is given in
Table C207A.7-L Exposure A has been included in
Table C207A . 7-1 as a reference that may be useful when
using the Wind Tunnel Procedure. Further information
on values ofz 0 in different types of terrain can be found
in Simiu and Scanlan (1996) and Table C207A.7-2
based on Davenport et ai (2000) and Wieringa et al.
(2001). The roughness classifications in Table C207A. 7-
2 are not intended to replace the use of exposure
categories as required in the code for structural design
purposes. However , the terrain roughness

classifications in Table C207A.7-2 may he related to
ASCE 7 exposure categories by comparing z Q values
between Table C207A. 7-1 and C207A. 7-2. For example,
the z 0 values for Classes 3 and 4 in Table C207A.7-2
fall within the range of z 0 values for Exposure C in
Table C207A.7-1. Similarly , the z 0 values for Classes 5
and 6 in Table C207A.7-2 fall within the range of z 0
values for Exposure B in Table C 2 07 A. 7-1.

Research described in Powell et al. (2003), Done lan et
ai (2004), and Vickery et al. (2008b) showed that the
drag coefficient over the ocean in high winds in tropical
cyclones did not continue to increase with increasing
wind speed as previously believed (e.g, Powell 1980).
These studies showed that the sea surface drag
coefficient , and hence the aerodynamic roughness of the
ocean , reached a maximum at mean wind speeds of
about 30m/s. There is some evidence that the drag

coefficient actually decreases (i.e., the sea surface
becomes aerodynamically smoother) as the wind speed
increases further (Powell et al 2003) or as the tropical
cyclone radius decreases (Vickery et al. 2008b). The
consequences of these studies are that the surface
roughness over the ocean in a tropical cyclone is
cons istent with that of exposure D rather than exposure
C. Consequently, the use of exposure D along the
tropical cyclone coastline is now required.

For Exposure B the tabulated values of K z correspond
to z 0 = 0.2 m, which is below the typical value of 0.3 m,
whereas for Exposures C and D they correspond to the
typical value of z 0 . The reason for the difference in
Exposure B is that this categoty of terrain , which is
applicable to suburban areas, often contains open
patches, such as highways, parking lots, and playing
fields. These cause local increases in the wind speeds at
their edges. By using an exposure coefficient
corresponding to a lower than typical value of z 0 , some
allowance is made for this. The alternative would be to
introduce a number of exceptions to use of Exposure B
in suburban areas , which would add an undesirable
level of complexity.

The value ofz 0 for a particular terrain can be estimated
from the typical dimensions of surface roughness
elements and their spacing on the ground area using an
empirical relationship, due to Lettau (1969), which is:

z 0 = 0. 5 H ob ?—■ (C207A. 7-1)

A 0 b

H 0 b = overage height of the roughness in

the upwind terrain

Bob ~ average vertical frontal area per

obstruction presented to the wind

A ob ~ the average area of ground occupied by
each obstruction, including the open
area surrounding it

Vertical frontal area is defined as the area of the
projection of the obstruction onto a vertical plane
normal to the wind direction. The area S ob may be
estimated by summing the approximate vertical frontal
areas of all obstructions within a selected area of
upwind fetch and dividing the sum by the number of
obstructions in the area. The average height H ob may
be estimated in a similar way by averaging the
individual heights rather than using the frontal areas.
Likewise A ob may be estimated by dividing the size of
the selected area of upwind fetch by the number of
obstructions in it.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

As an

single family homes with typical height H ob = 6m,
vertical frontal area (including some trees on each lot)
of 1 00m 2 , and ground area per home of } ,000m 2 , then
z 0 is calculated to be z 0 ~ 0.5 x 20 x 100/1,000 =
. ' 0.3 m, which falls into exposure category B according to
Table C2Q7A.7-1.

Trees and bushes are porous and are deformed by
strong winds, which reduce their effective frontal areas
(ESDI), 1993). For conifers and other evergreens no
) more than 50 percent of their gross frontal area can be
taken to be effective in obstructing the wind. For
; deciduous trees and bushes no more than 15 percent of
their gross frontal area can be taken to be effective in
obstructing the wind. Gross frontal area is defined in
l this context as the projection onto a vertical plane
v (normal to the wind) of the area enclosed by the
\ envelope of the tree or bush.

fjio (1992) estimated that the majority of buildings
/(perhaps as much as 60 percent to 80 percent) have an
(exposure categoiy corresponding to Exposure B. While

//suffice far most practical applications , oftentimes the
'//designer is in need of additional information ,

'for clearings (e.g, large parking lots y freeways, or tree
/(/clearings) in the othenvise ", normal ” ground surface
roughness B. The following is offered as guidance for
these situations:

Mere ■ S'

fffhe simple definition of Exposure B given in the body of
the code, using the surface roughness categoiy
definition, is shown pictorially in Figure C207A.7-L
fifihis definition applies for the surface roughness B
Condition prevailing 800 m upwind with insufficient
/*' open patches " as defined in the following text to
disqualify the use of Exposure B.

An opening in the surface roughness B large enough to
fffipve a significant effect on the exposure category

■

CHAPTER 2 - Minimum Design Loads 2-37

determination is defined as an " open patch . ” An open
patch is defined as an opening greater than or equal to
approximately 50 m on each side (i.e., greater than
50 m by 50 m). Openings smaller than this need not be
considered in the determination of the exposure
categoiy.

The effect of open patches of surface roughness C or D
on the use of exposure categoiy B is shown pictorially
in Figures C207A. 7-3 and C207A. 7-4. Note that the plan
location of any open patch may have a different effect
for different wind directions.

Aerial photographs, representative of each exposure
type, are included in the commentary to aid the user in
establishing the proper exposure for a given site.
Obviously, the proper assessment of exposure is a
matter of good engineering judgment. This fact is
particularly true in light of the possibility that the
exposure could change in one or more wind directions
due to future demolition and/or development .

207A.7.1 Wind Directions and Sectors

For each selected wind direction at which the wind loads
are to be determined, the exposure of the building or
structure shall be determined for the two upwind sectors
extending 45° either side of the selected wind direction*
The exposure in these two sectors shall be determined in
accordance with Sections 207 A. 7. 2 and 207 A. 7. 3, and the
exposure whose use would result in the highest wind loads
shall be used to represent the winds from that direction.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-38

CHAPTER 2 - Minimum Design Loads

Notes:

1 . Values are nominal design 3-second gust wind speeds in kilometers per hour at 1 0 m above ground for Exposure C category.

2. Linear interpolation between contours is permitted.

3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area.

4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions.

5. Wind speeds correspond to approximately a 1 5% probability of exceedance in 50 years (Annual Exceedance Probability = 0.00333, MR1 = 300 years).

6. Results are from PAGASA.

Figure 207A.5-1 A Basic Wind Speeds for Occupancy Category III, IV and V Buildings and Other Structures
Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-39

Notes:

1- Values are nominal design 3-second gust wind speeds in kilometers per hour at 10 m above ground for Exposure C category.

2. Linear interpolation between contours is permitted.

2. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area.

4- Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions.

5. Wind speeds correspond to approximately a 7% probability of exceedance in 50 years (Annual Exceedance Probability = 0.00143, MRI = 700 years).
6- Results are from PAG AS A.

Figure 207A.5-1B Basic Wind Speeds for Occupancy Category II Buildings and Other Structures
National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-40

CHAPTER 2 - Minimum Design Loads

Notes:

1. Values are nominal design 3-second gust wind speeds in kilometers per hour at 10 m above ground for Exposure C category.

2. Linear interpolation between contours is permitted.

3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area.

4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions.

5. Wind speeds correspond to approximately a 3% probability of exceedance in 50 years (Annual Exceedance Probability = 0.000588, MRI = 1700
years).

6. Results are from PAGASA.

Figure 207A.5-1C Basic Wind Speeds for Occupancy Category I Buildings and Other Structures

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-41

WIND

F/i< 18m, d x a 450 m

For h > 18m, d, > greater of 790 m or 20 h

BUILDING OR
OTHER STRUCTURE

ANY ROUGHNESS ROUGHNESS B

njriTLRJTJTJluTJT^^

L J

ANY ROUGHNESS

Figure C2U/A.7-1

Upwind Surface Roughness Conditions Requires for Exposure B.

|< >

(a)

WIND

> greater of 790 m or 20 h, and
d 2 ^ greater of 1 80 m or 20 h

BUILDING OR
OTHER STRUCTURE

ANY ROUGHNESS

ROUGHNESS D

ROUGHNESS B AND/OR C
™JTJTJTJTJTJT^

ANY ROUGHNESS

(b)

Figure C207A.7-2

Upwind Surface Roughness Conditions Required for Exposure D, for the Cases with
(a) Surface Roughness D Immediately Upwind of the Building, and (b) Surface Roughness B and/or C Immediately

Upwind of the Building

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-42 CHAPTER 2 - Minimum Design Loads

Table 207 A. 6-1

Wind Directionality Factor, K d

Structure Type

Directionality Factor K d *

Buildings

Main Wind Force Resisting System

0.85

Components and Cladding

0.85

Arched Roofs

0.85

Chimneys, Tanks, and Similar Structures

Square

0.90

Hexagonal

0.95

Round

0.95

Solid Freestanding Walls and Solid

0.85

Freestanding and Attached Signs

Open Signs and Lattice Framework

0.85

Trussed Towers

Triangular, square, rectangular

0.85

All other cross sections

0.95

* Directionality Factor K d has been calibrated with combinations of loads
specified in Section 203. This factor shall only be applied when used in
conjunction with load combinations specified in Sections 203.3 and 203.4.

207A.7.2 Surface Roughness Categories

A ground Surface Roughness within each 45° sector shall
be determined for a distance upwind of the site as defined
in Section 207A.7.3 from the categories defined in the
following text, for the purpose of assigning an exposure
category as defined in Section 207A.7.3.

Surface Roughness B: Urban and suburban areas, wooded
areas, or other terrain with numerous closely spaced
obstructions having the size of single-family dwellings or
larger.

Surface Roughness C: Open terrain with scattered
obstructions having heights generally less than 9 m. This
category includes flat open country and grasslands.

Surface Roughness D: Flat, unobstructed areas and water
surfaces. This category includes smooth mud flats, salt
flats, and unbroken ice.

207A.7.3 Exposure Categories

Exposure B: For buildings with a mean roof height of less
than or equal to 9 m, Exposure B shall apply where the
ground surface roughness, as defined by Surface
Roughness B, prevails in the upwind direction for a
distance greater than 450 m. For buildings with a mean roof
height greater than 9 m, Exposure B shall apply where
Surface Roughness B prevails in the upwind direction for
a distance greater than 790 m or 20 times the height of the
building, whichever is greater.

Exposure C: Exposure C shall apply for all cases where
Exposures B or D do not apply.

Exposure D: Exposure D shall apply where the ground
surface roughness, as defined by Surface Roughness D,
prevails in the upwind direction for a distance greater than
1500 m or 20 times the building height, whichever is
greater. Exposure D shall also apply where the ground
surface roughness immediately upwind of the site is
exposure B or C, and the site is within a distance of 180 in
or 20 times the building height, whichever is greater, from

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-43

miMfa Exposure D condition as defined in the previous
jjSll lntence.

®For a site located in the transition zone between exposure
3jj|%ate<mries. the category resulting in the largest wind forces
shall be used.

xluitc exposure between the preceding
, permitted in a transition zone provided that it
is determined by a rational analysis method defined in the
recognized literature.

207A.7.4 Exposure Requirements

iiMommentaiy:

■■:■■■■ ■:■■■■■ : ' •

provision in Section 207A.5J requires that a
'■Mifmcture be designed for winds from all directions . A
Rational procedure to determine directional wind loads
follows. Wind load for buildings using Section
MiOJBAJ and Figures 207B.4-I, 207B.4-2 or 207B.4-3
determined for eight wind directions at 45°
'Sfptervals. with four falling along primary building axes
| shown in Figure C207A.7-5 . For each of the eight
I directions, upwind exposure is determined for each of
b'45° sectors, one on each side of the wind direction
i§mis. The sector with the exposure giving highest loads
f&^ill be used to define wind loads for that direction. For
I} fmample f for winds from the north , the exposure from
§Jff | cior one or eight, whichever gives the higher load, is
For wind from the east, the exposure from sector
|j|f | (dor three, whichever gives the highest load, is used.
|||®r wind coming from the northeast, the most exposed

of sectors one or two is used to determine full X and y
loading individually . and then 75 percent of these loads
are to be applied in each direction at the same time
according to the requirements of Section 207B.4.6 and
Figure 2 07 B. 4-8. The procedure defined in this section
for determining wind loads in each design direction is
not to be confused with the determination of the wind
directionality factor K d . The K d factor determined from
Section 207 A. 6 and Table 207 A. 6- J applies for all
design wind directions. See Section C207A.6.

Wind loads for cladding and low-rise buildings elements
are determined using the upwind exposure for the single
surface roughness in one of the eight sectors of
Figure C207A.7-5 that gives the highest cladding
pressures.

Figure C207A.7-5
Determination of Wind Loads
from Different Directions

National Structural Code of the Philippines Volume i, 7th Edition, 2015

CHAPTER 2 - Minimum Design Loads

BUILDING OR OTHER
STRUCTURE

WIND

SURFACE ROUGHNESS

LENGTH OF OPEN I
PATCHES

X = 1000 in

“OPEN PATCHES” - OPENINGS > 50 m x 50 m
d lt d 2 ,_, d t > SO m
d 1 + d 2 +_ + d i < 200 m

TOTAL LENGTH OF SURFACE ROUGHNESS B> 800 m
WITHIN 1000 m OF UPWIND FETCH DISTANCE

Figure C207A.7-3

Exposure B with Upwind Open Patches

Association of Structural Engineers of the Philippines, Inc. (ASEP)

2-46 CHAPTER 2 - Minimum Design Loads

207A.7A1 Directional Procedure (Section 207B)

For each wind direction considered, wind loads for the
design of the MWFRS of enclosed and partially enclosed
buildings using the Directional Procedure of Section 207B
shall be based on the exposures as defined in Section
207A.7.3. Wind loads for the design of open buildings with
monoslope, pitched, or troughed free roofs shall be based
on the exposures, as defined in Section 207A.7.3, resulting
in the highest wind loads for any wind direction at the site.

207A.7.4.2 Envelope Procedure (Section 207C)

Wind loads for the design of the MWFRS for all low-rise
buildings designed using the Envelope Procedure of
Section 207C shall be based on the exposure category
resulting in the highest wind loads for any wind direction
at the site.

207A.7.4.3 Directional Procedure for Building
Appurtenances and Other Structures
(Section 207D)

Wind loads for the design of building appurtenances (such
as rooftop structures and equipment) and other structures
(such as solid freestanding walls and freestanding signs,
chimneys, tanks, open signs, lattice frameworks, and
trussed towers) as specified in Section 207D shall be based
on the appropriate exposure for each wind direction
considered.

207A.7.4.4 Components and Cladding (Section 207E)

Design wind pressures for components and cladding shall
be based on the exposure category resulting in the highest
wind loads for any wind direction at the site.

207 A.8 Topographic Effects

Commentary:

As an aid to the designer , this section was rewritten in
ASCE 7-98 to specify when topographic effects need to be
applied to a particular structure rather than when they do
not as in the previous version. In an effort to exclude
situations where little or no topographic effect exists ,
Condition (2) was added to include the fact that the
topographic feature should protrude significantly above
(by a factor of two or more) upwind terrain features before
it becomes a factor. For example, if a significant upwind
terrain feature has a height of 10 m above its base elevation
and has a top elevation of 30 m above mean sea level then
the topographic feature (hill, ridge , or escarpment) must
have at least the H specified and extend to elevation 52 m

mean sea level (30.5 m + [3.22 x 10.7 mj) within the 3.22-
km radius specified.

A wind tunnel study by Means et al (1 996) and observation
of actual wind damage has shown that the affected height
II is less than previously specified. Accordingly, Condition
(5) was changed to 4.5 m in Exposure C.

Buildings sited on the upper half of an isolated hill or
escarpment may experience significantly higher wind
speeds than buildings situated on level ground. To account
for these higher wind speeds, the velocity pressure
exposure coefficients in Tables 207 B. 3-1, 207 C. 3-1,
207D.3-1, and 207E.3-1 are multiplied by a topographic
factor , K zt , determined by Equation 207A.S-L The
topographic feature (2-D ridge or escarpment, or 3-D
axisymmetrical hill) is described by two parameters, H and
L h . H is the height of the hill or difference in elevation
between the crest and that of the upwind terrain. is the
distance upwind of the crest to where the ground elevation
is equal to half the height of the hill. K zt is determined from
three multipliers, K\, K 2 , and which are obtained from
Figure 207A.8-1, respectively. is related to the shape
of the topographic feature and the maximum speed-up near
the crest, K 2 accounts for the reduction in speed-up with
distance upwind or downwind of the crest, and
accounts for the reduction in speed-up with height above
the local ground surface.

The multipliers listed in Figure 207 A. 8-1 are based on the
assumption that the wind approaches the hill along the
direction of maximum slope , causing the greatest speed-up
near the crest. The average maximum upwind slope of the
hill is approximately H/2Lf t , and measurements have
shown that hills with slopes of less than about
0.10 (. H/L h < 0.20) are unlikely to produce significant
speed-up of the wind. For values of H/Lh > 0.5 the
speed-up effect is assumed to be independent of slope. The
speed-up principally affects the mean wind speed rather
than the amplitude of the turbulent fluctuations, and this
fact has been accounted for in the values ofK x , K 2 , and
/<3 given in Figure 207A.8-1 . Therefore, values of K zt
obtained from Figure 207A.8-1 are intended for use with
velocity pressure exposure coefficients, K h and K z , which
are based on gust speeds .

It is not the intent of Section 207 A.8 to address the general
case of wind flow over hilly or complex terrain for which
engineering judgment, expert advice, or the Wind Tunnel
Procedure as described in Section 207F may be required.
Background material on topographic speed-up effects may
be found in the literature (Jackson and Hunt 1975, Lemelin
et al. 1988, and Walmsley et al. 1 986).

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-47

The designer is cautioned that , at present, the code
contains no provision for vertical wind speed-up because
of a topographic effect, even though this phenomenon is
known to exist and can cause additional uplift on roofs.
Additional research is required to quantify this effect
before it can be incorporated into the code.

207A.8.1 Wind Speed-Up over Hills, Ridges, and
Escarpments

Wind speed-up effects at isolated hills, ridges, and
escarpments constituting abrupt changes in the general
topography, located in any exposure category, shall be
included in the design when buildings and other site
conditions and locations of structures meet all of the
following conditions:

111. The hill, ridge, or escarpment is isolated and
unobstructed upwind by other similar topographic
features of comparable height for 100 times the height
of the topographic feature (100f/) or 3.2 km,
whichever is less. This distance shall be measured
horizontally from the point at which tire height H of
the hill, ridge, or escarpment is determined.

2. The hill, ridge, or escarpment protrudes above the
height of upwind terrain features within a 3.2-km
radius in any quadrant by a factor of two or more.

3. The structure is located as shown in Figure 207A.8-1
in the upper one-half of a hill or ridge or near the crest
of an escarpment.

4. H/L h > 0.2.

5. H is greater than or equal to 4.5 m for Exposure C and
D and 18 m for Exposure B.

207A.8.2 Topographic Factor

The wind speed-up effect shall be included in the

calculation of design wind loads by using the factor K zt :

Kzt = (1 + Kl + +■ K3) 2

(207A.8-1)

where K 2 , K 2 , and K 3 are given in Figure 207A.8-1.

If site conditions and locations of structures do not meet all
the conditions specified in Section 207A.8.1 then

K xt = 1 . 0 .

ESCARPMENT

2-D RIDGE OR 3-D AXISYMMETRICAL HILL

Figure 207A.8-1
Topographic Factor, K zt

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2 “48 CHAPTER 2 - Minimum Design Loads

Table 207A.8-1

Topographic Multipliers for Exposure C

/Ci Multiplier

2-D

Ridge

2-D

Escarp.

3-D

Axisym.

I< 2 Multiplier

ri i " ah

/<T Multiplier

0.00

0.26

0.50

0.32

1.00

0.37

1.50

0.42

2.00

0.47

2.50

0.53

3.00

3.50

4.00

2-D

Escarp.

LOO

0,88

0.75

0.63

0.50

0.38

.25

.13

.00

Other

Cases

2-D

Ridge

2-D

Escarp.

1.00

3-D

Axisym.

Hill

1.00

1 . For values of H/L fl> x/L fx and z/L tl other than those shown, linear interpolation is permitted.

2. For j- > 0.50, assume = 0. 50 for evaluating and substitute 2 H for L ft for evaluating l< 2 and K 3 .

**l i L h

3. Multipliers arc based on the assumption that wind approaches the hill or escarpment along the direction of maximum slope.

4. Notation:

Equations:

{ “ Height of hill or escarpment relative to the upwind terrain, in meters.

h - Distance upwind of crest to where the difference in ground elevation is half the height of J

\ - Factor to account for shape of topographic feature and maximum speed-up effect.

2 - Factor to account for reduction in speed-up with distance upwind or downwind of crest.

3 = Factor to account for reduction in speed-up with height above local terrain.

: = Distance (upwind or downwind) from the crest to the building site, in meters.

: = Height above ground surface at building site, in meters,

i = Horizontal attenuation factor.

' ” Height attenuation factor.

K zt = (1 + Ki + I< 2 + K 3 ) 2
K t determined from table below

*•■(*-£)

l( 3 = e-r* /L *

l or escarpment, in meters.

Hill Shape

2-dimensional ridges

(or valleys with negative)

H in KJW/Lk)

2- dimensional escarpments

3- dimensional axisymmetrical hill

KiimiMi

Exposure

Upwind

Downwind

of Crest

1.30

1.45

1.55

3.00

1.50

0.75

0.85

0.95

2.50

1.50

4.00

0.95

1.05

1.15

4.00

1.50

Figure 207A.8-2

Parameters for Speed-Up Over Hills and Escarpments

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-49

207A.9 Gust Effects

: Commentary:

' • •

f/SCP 2001 contains a single gust effect factor of 0,85
Ifor rigid buildings . As an option , the designer can
> || corporate specific features of the wind environment
and building size to more accurately calculate a gust
effect factor. One such procedure is located in the body
\ of the standard (Solari 1993a and 1993b). A procedure
is also included for calculating the gust effect factor for

• flexible structures. The rigid structure gust factor is 0
percent to 10 percent lower than the simple, but

• conservative, value of 0. 85 permitted in the code without
calculation. The procedures for both rigid and flexible
structures (1) provide a superior model for flexible
structures that displays the peak factors g Q and g R and

' (2) cause the flexible structure value to match the rigid
structure as resonance is removed. A designer is free to
use any other rational procedure in the approved
; literature, as stated in Section 207A.9.5.

the fundamental model shape

(z/Ii)t

the mode exponent

—

air density

Cfx

mean along-wind force coefficient

modal mass

I p(z')4> 2 (z)dz

J o

p(z)

mass per unit height

—

(1.65)“/(a + f +1)

and V% i,

s the 3-s gust speed at height z. This can

evaluated by V 2 = b(zf 33) a V, where V is the 3-s gust
speed in Exposure C at the reference height (obtained
from Figure 207 A. 5-1); b and a are given in
Table 207A.9-1.

RMS Along-Wind Acceleration * The rms along-wind
acceleration <J x {z) as a function of height above the
ground surface is given by:

l The gust effect factor accounts for the loading effects in
•;|j the along-wind direction due to wind turbulence-
structure interaction. It also accounts for along-wind
loading effects due to dynamic amplification for flexible
f buildings and structures. It does not include allowances
for across-wind loading effects , vortex shedding,
instability due to galloping or flutter , or dynamic
torsional effects. For structures susceptible to loading
y effects that are not accounted for in the gust effect
: factor, information should be obtained from recognized
literature (Kareem 1992 and 1985, Gurley and Kareem
<1993, Solari 1993a and 1993b, and Kareem and Smith
21994) or from wind tunnel tests .

Along-Wind Response. Based on the preceding
de finition of the gust effect factor, predictions of along
[ wind response, for example, maximum displacement,
root-mean-square (rms), and peak acceleration, can he
made. These response components are needed for
\ survivability and serviceability limit states. In the
following, expressions for evaluating these along-wind
response components are given.

Maximum Along-Wind Displacement The maximum
along-wind displacement X max (z) as a function of
height above the ground surface is given by:

(C207A.9-2)

where V 2 is the mean hourly wind speed at height z, m/s:

— — / z \ s

(C207A.9-3)

where b and a are defined in Table 2 07 A. 9-1.

Maximum Along-Wind Acceleration . The maximum
along-wind acceleration as a function of height above
the ground surface is given by:

~~ Ex&x ( z 0

0.5772

Ex “ ItiiyifT) 4*

yj 2 IniiixT)

(G207A.9-4)

(C207A.9-5)

where T = the length of time over which the minimum
acceleration is computed, usually taken to be 3, 600 s to
represent l hour.

Xmaxiz)

where

<l)(z)pBhC fx Vi

2m 1 (27rn 1 ) 2

Approximate Fundamental Frequency. To estimate the
KG (C207A.9-1) dynamic response of structures , knowledge of the

fiindamental frequency (lowest natural frequency) of the
structure is essential. This value would also assist in
determining if the dynamic response estimates are
necessary. Most computer codes used in the analysis of
National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-50 CHAPTER 2 - Minimum Design Loads

structures would provide estimates of the natural
frequencies of the structure being analyzed. However ,
for the preliminary design stages some empirical
relationships for building period T a (T a = 1 fn x ) are
available in the earthquake chapters of ASCE 7.
However \ it is noteworthy that these expressions are
based on recommendations for earthquake design with
inherent bias toward higher estimates of fundamental
frequencies (Goel and Chopra 1997 and 1998). For
wind design applications these values may be
unconservative because an estimated frequency higher
than the actual frequency would yield lower values of
the gust effect factor and concomitantly a lower design
wind pressure. However \ Goel and Chopra (1997 and
1 998) also cite lower bound estimates of frequency that
are more suited for use in wind applications . These
lower-bound expressions are now given in Section
207 A. 9. 2; graphs of these expressions are shown in

on regular buildings , limitations based on height and
slenderness are required. The effective length L e ff, uses
a height-weighted average of the along-wind length of
the building for slenderness evaluation. The top portion

of the building is most important; hence the height -
weighted average is appropriate. This method is an
appropriate first-order equation for addressing
buildings with setbacks . Explicit calculation of gust
effect factor per the other methods given in Section
207A.9 can still be performed.

Observation from wind tunnel testing of buildings where
frequency is calculated using analysis software reveals
the following expression for frequency, appropriate for
buildings less than about 120 m in height , applicable to
all buildings in steel or concrete:

n t = 100/// (m) average value

(C207A.9-6)

n i = 75 /H (m) lower bound value (C 207 A. 9-7)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-51

Equation €207 A. 9-7 for the lower bound value is
provided in Section 207 A. 9.2. ; .

gphsed on fill-scale measurements of buildings under the
action of wind ' the following expression has been
proposed for wind applications (Zhou and Kareem
2001. Zhou t Kijewski, and Kareem 2002):

m = iso///

( C207A.9-8)

This frequency expression is based on older buildings
and overestimates the frequency common in U.S.
construction for smaller buildings less than 120 m in
height, but becomes more accurate for tall buildings
/ greater than 120 m in height. The Australian and New
Zealand Standard AS/NZS 1170.2 , Eurocode ENV 1991-
2 - 4 , Hong Kong Code of Practice on Wind Effects
(2004), and others have adopted Equation C207A.9-8
for all building types and all heights .

Recent studies in Japan involving a suite of buildings
under low-amplitude excitations have led to the
following expressions for natural frequencies of
buildings (Sataka et al 2003):

Ijrii — 220/ H(m) (concrete buildings) (C207A.9-9)

ff|f== 164 /H(m) (steel buildings)

(C207A.9-10)

The expressions based on Japanese buildings result in

general expression given in Equations C207A.9-6
^through C207A.9-S, particularly since the Japanese
data set has limited observations for the more flexible
thuddings sensitive to wind effects and Japanese
construction tends to be stiffen.

lEbr cantilevered masts or poles of uniform cross-section
On which bending action dominates):

n t = (0.56 /h 2 )T(W/m) (C207A.9-1 1)

the mass /unit heights (This formula may be used for
masts with a slight taper, using average value of El and
m) (ECCS 1978).

Jti approximate formula for cantilevered / tapered ,
Nrcular poles (ECCS 1978) is:

n t ■"== [A/ (2nh 2 )]y/(EI/rn) (C207A.9-12)

where h is the height, and E, /, and m are calculated
for the cross-section at the base. A depends on the wall
thicknesses at the tip and base, e t and and external
diameter at the tip and base, d t and d b , according to the
following formula:

[ H 1 9 “"( W\ '

■■■■ (C207A.9-13)

Equation C207A.9-12 reduces to Equation C207A.9-11
for uniform masts. For free-standing lattice towers
(without added ancillaries such as antennas or lighting
frames) (Standards Australia 1994):

l lsbo^/Zi 2 (C207A 9-14)

where w a is the average width of the structure in mand
h is tower height An alternative formula for lattice
towers (with added ancillaries) (Wyatt 1984) is:

= (^) 2/3 (^) 1/2 (C207A.9-15)

where = tower base width and L N = 270 m for
square base towers, or 230 rnfor triangular base towers.

Structural Damping. Structural damping is a measure
of energy dissipation in a vibrating structure that results
in bringing the structure to a quiescent state. The
damping is defined as the ratio of the energy dissipated
in one oscillation cycle to the maximum amount of
energy in the structure in that cycle. There are as many
structural damping mechanisms as there are modes of
converting mechanical energy into heat. The most
important mechanisms are material damping and
interfacial damping:

In engineering practice, the damping mechanism is
often approximated as viscous damping because it leads
to a linear equation of motion. This damping measure,
in terms of the damping ratio, is usually assigned based
on the construction material, for example, steel or
concrete. The calculation of dynamic load effects
requires damping ratio as an input. In wind
applications , damping ratios of l percent and 2 percent
are typically used in the United States for steel and
concrete buildings at serviceability levels, respectively,

6.65

°- 9 + (S)

0.666

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-52 CHAPTER 2 - Minimum Design Loads

while ISO (1997) suggests 1 percent and 1.5 percent for
steel and concrete, respectively . Damping values for
steel support structures for signs, chimneys, and towers
may he much lower than buildings and may fall in the
range of (l 15 percent to 0.5 percent Damping values of
special structures like steel stacks can be as low as OJ
percent to 0.6 percent and 0.3 percent to 1.0 percent for
unlined and lined steel chimneys, respectively (ASME
1992 and CICIND 1999). These values may provide
some guidance for design . Damping levels used in wind
load applications are smaller than the 5 percent
damping ratios common in seismic applications because
buildings subjected to wind loads respond essentially
elastically whereas buildings subjected to design level
earthquakes respond inelastically at higher damping
levels.

Because the level of structural response in the
serviceability and survivability states is different , the
damping values associated with these states may differ.
Further, due to the number of mechanisms responsible
for damping, the limited full-scale data manifest a
dependence on factors such as material height \ and type
of structural system and foundation. The Committee on
Damping of the Architectural Institute of Japan suggests
different damping values for these states based on a
large damping database described in Sataka et ah
(2003).

In addition to structural damping, aerodynamic
damping may he experienced by a structure oscillating
in air. In general the aerodynamic damping
contribution is quite small compared to the structural
damping, and it is positive in low to moderate wind
speeds. Depending on the structural shape, at some
wind velocities, the aerodynamic damping may become
negative, which can lead to unstable oscillations. In
these cases, reference should be made to recognized
literature or a wind tunnel study.

Alternate Procedure to Calculate Wind Loads .
The concept of the gust effect factor implies that the
effect of gusts can be adequately accounted for by
multiplying the mean wind load distribution with height
by a single factor. This is an approximation. If a more
accurate representation of gust effects is required, the
alternative procedure in this section can be used. It
takes account of the fact that the inertial forces created
by the building '$ mass, as it moves under wind action,
have a different distribution with height than the mean
wind loads or the loads due to the direct actions of gusts
(ISO 1997 and Sataka et ai 2003). The alternate
formulation of the equivalent static load distribution
utilizes the peak base bending moment and expresses it
in terms of inertial forces at different building levels. A
base bending moment, instead of the base shear as in

earthquake engineering \ is used for the wind loads, as it
is less sensitive to deviations from a linear mode shape
while still providing a gust effect factor generally equal
to the gust factor calculated by the Section 207 NSCP
2010 standard. This equivalence occurs only for
structures with linear mode shape and uniform mass
distribution, assumptions tacitly implied in the previous
formulation of the gust effect factor, and thereby permits
a smooth transition from the existing procedure to the
formulation suggested here . For a more detailed
discussion on this wind loading procedure, see ISO
(1997) and Sataka et al (2003).

Along-Witul Equivalent Static Wind Loading .
The equivalent static wind loading for the mean,
background , and resonant components is obtained using
the procedure outlined in the following text.

Mean wind load component P } at the J th floor level is
given by:

Pj ~ qjXC p xAjXG (C207A.9-16)

where

j - floor level

Zj = height of the J th floor above the ground

level

qj “ velocity pressure at height Zj

C p = external pressure coefficient

G = 0 , 925(1 + 1 .7g v hY x Is the gust

velocity factor

Peak background wind load component P at the J th
floor level is given similarly by:

(C207A.9 -17)

where

Gb = 0 925 ( 1-7/2 Bq< * )

0 925 \t + 1.7 g v lrj

— is the background component of the gust
effect factor.

Peak resonant wind load component Prj at the J th floor
level is obtained by distributing the resonant base
bending moment response to each level

Pnj = C Mj m n (C2Q7A.9-18)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-53

M/ 'ZWjfyZj

(C207A.9-19)

MGn

M »=-r

(C207A.9-20)

Z p ' z '-

/=l,n

(C207A9-21)

where

J Mj

m r =

Wj v:l = -

n =
=

vertical load distribution factor

peak resonant component of the base

bending moment response

portion of the total gravity load of the

building located or assigned to level /

total stories of the building

first structural mode shape value at level j

mean base bending produced by mean

wind load

G r = 0.925 1

>1 + 1 . 7g v tJ

liiiv-Z - is the resonant i component of the gust
■ effect factor.

Along- Wind Response . Through a simple static
0nalySis the peak-building response v alongAvhid
direction can be obtained by:

(C207A.9-22)

where r, r B , and f R = mean, peak background, and

shear forces, moment, or displacement. Once the
equivalent static wind load distribution is obtained, any
response component ; including acceleration " can be
obtained using a simple static analysis: It is suggested
that caution must be exercised when combining the
loads instead of response according to the preceding
expression, for example,

'■Pj,= Pj +

(C207A.9-2 3)

because the background and the resonant load
components have normally different distributions along

the building height. Additional background can be found
in ISO ( 1997) and Sataka et ah (2003).

Example: The following example is presented^ to
illustrate the calculation of the gust effect factor. Table
C207A.9-1 uses the given information to obtain values
from Table 2 07 A. 9-1. Table C20 7 A. 9-2 presents the
calculated values. Table C2 0 7 A.9^3: summarizes the
calculated displacements and acceleration* ■■■as^-a-
function of the height Z-

Given Values:

Basic wind speed at reference
height in exposure C

150 km/h

c fx

y \

1.3 ';0.

Damping ratio

0.01

Mode exponent

1.0

Type of exposure

. : =V

Building height h

v-v.' « ;■

183: m f|v

Building width B

cim-]

30.5m:

Building depth L

30.5 m

Building natural frequency n t

0.2 Hz

Building density

12 lb/ft 3
192.0817
kg/m 3

Air density

1.2369

kg/m 3

Table C207A.9-1
Calculated Values

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-54 CHAPTER 2 - Minimum Design Loads

Q z

v- z

N i
R„

Table C207A.9-2
Calculated Values

40.23 m/s
109.73m
0.201
216.75 m
0.616
32. 95 m/s
47.59 m/s
1.31
0.113
0.852

R 2

0.610

5.113

0.176

2.853

0.289

0.813

1.062

0.501

10.88x10 6
kg

3.787

Table 207A.9-3

Floor

Zj (m)

^maxj

RMS Acc.*

( m / s 2 )

RMS Acc. *

(mg)

Max Acc. *

( m / s 2 )

Max Acc.

(mg)

18.29

0.10

0.03

0.00

0.41

0.02

1.6

36.58

0.20

0.06

0.01

0.83

0.03

3.1

54.86

0.30

0.09

0.01

1.24

0.05

4.7

73.15

0.40

0.13

0.02

1.66

0.06

6.3

91.44

0.50

0.16

0.02

2.07

0.08

7.8

109.73

0.60

0.19

0.02

2.49

0.09

9.4

128.02

0.70

0.22

0.03

2.90

0.11

11.0

146.3

0.80

0.25

0.03

3.32

0.12

12.6

164.59

O.SO

0.28

0.04

3.73

0.14

14.1

182.88

1.00

0.31

0.04

4.14

0.15

15.7

Aerodynamic Loads on Tall Buildings — An
Interactive Database . Under the action of wind, tall
buildings oscillate simultaneously in the along-wind,
across -wind, and torsional directions. While the along-
wind loads have been successfully treated in terms of
gust loading factors based on quasi-steady and strip
theories, the across-wind and torsional loads cannot be
treated in this manner, as these loads cannot be related
in a straightforward manner to fluctuations in the
approach flow. As a result, most current codes and
standards provide little guidance for the across-wind
and torsional response ISO (1997) and Sataka et ai
(2003).

To provide some guidance at the prelimiruvy design
stages of buildings , an interactive aerodynamic loads
database for assessing dynamic wind-induced loads on
a suite of generic isolated buildings is introduced.
Although the analysis based on this experimental
database is not intended to replace wind tunnel testing
in the final design stages , it provides users a
methodology to approximate the previously untreated

across-wind and torsional responses in the early design
stages. The database consists of high frequency base
balance measurements involving seven rectangular
building models , with side ratio D/B, where D is the
depth of the building section along the oncoming wind
direction) from 1/3 to 3 , three aspect ratios for each
building model in two approach flows ; namely ,
BL t (a = 0, 16) andBL 2 (a = 0. 35) corresponding to
an open and an urban environment. The data are
accessible with a user-friendly Java-based applet
through the worldwide Internet community at
http://aerodata. cejid.edu/interface/interface. html

Through the use of this interactive portal users can
select the geometry and dimensions of a model building
from the available choices and specify an urban or
suburban condition. Upon doing so, the aerodynamic
load spectra for the along-wind, across-wind, or
torsional directions is displayed with a Java interface
permitting users to specify a reduced frequency
(building frequency x building dimension/ wind
velocity) of interest and automatically obtain the

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-55

corresponding spectral value . When coupled with the
{supporting Web documentation, examples, and concise
analysis procedure , the database provides a
comprehensive tool for computation of wind-induced
response of tall buildings, statable as a design guide in
the preliminary stages .

;

Example: An example tall building is used to
demonstrate the analysis using the database. The
building is a square steel tall building with size H x W t
x IV 2 ~ 200 x 40 x 40 m and an average radius of
gy ration of IS m.

■

The three fundamental mode frequencies, f lt are 0.2,

0.2, and 035 Hz in X, Y, and Z directions, respectively ;
I the mode shapes are all linear, or (3 is equal to 1.0, and
there is no modal coupling. The building density is equal
to 250 kg/ m*. This building is located in Exposure A or
close to the Sl 2 test condition of the Internet-based
database (Zhou et ai 2002), In this location
(Exposure A), the reference 3-sec design gust speed at a
50-year recurrence interval is 63 m/s [ASCE 7-98],
which is equal to 18.9 m/s upon conversion to 1-h mean
wind speed with 50-yr MRI (207 * 030 = 62 m/s). For
- serviceability requirements, 1-h mean wind speed with
' I0-yr MRI is equal to 14 m/s (207 x 030 * 0.74 = 46).

' For the sake of illustration only, the first mode critical
structural damping ratio, < r 1 . is to be 0.01 for both
'survivability and serviceability design.

. Using these aerodynamic data and the procedures
) provided on the Web and in ISO (1997), the wind load
: effects are evaluated and the results are presented in
Table C207A. 9-4. This table includes base moments and
acceleration response in the along-wind direction
; obtained by the procedure in ASCE 7-02. Also the
building experiences much higher across-wmd load
effects when compared to the along-wind response for
this example, which reiterates the significance of wind
i loads and their effects in t he across -wind direction.

' ■

207A.9.1 Gust Effect Factor

The gust-effect factor for a rigid building or other structure
is permitted to be taken as 0*85.

207A.9.2 Frequency Determination

To determine whether a building or structure is rigid or
flexible as defined in Section 207A.2, the fundamental
natural frequency, n ly shall be established using the
structural properties and deformational characteristics of
hie resisting elements in a properly substantiated analysis.

■

Low-Rise Buildings, as defined in 207 A.2, are permitted to
be considered rigid.

207A.9.2.1 Limitations for Approximate Natural
Frequency

As an alternative to performing an analysis to determine
n 1 , the approximate building natural frequency, n ly shall
be permitted to be calculated in accordance with Section
207A.9.3 for structural steel, concrete, or masonry
buildings meeting the following requirements:

1. The building height is less than or equal to 91 m, and

2. The building height is less than 4 times its effective
length, L e ff .

The effective length, L e ff y in the direction under
consideration shall be determined from the following
equation:

I \

L eff~

Z"=l Mi

lUhi

(207A.9-1)

The summations are over the height of the building
where

hi ~ is the height above grade of level i

Li = is the building length at level i parallel to the

wind direction

207A.9.3 Approximate Natural Frequency

The approximate lower-bound natural frequency (n a ), in
Hertz, of concrete or structural steel buildings meeting the
conditions of Section 207A.9.2.1, is permitted to be
determined from one of the following equations:

For structural steel moment-resisting-frame buildings:

n a = 22.2 //i 08 (207A.9-2)

For concrete moment-resisting frame buildings:

n a — 43.5//1 0,9 (207 A. 9-3)

For structural steel and concrete buildings with other
lateral-force-resisting systems:

n a = 75/ft (207A.9-4)

National Structural Code of the Philippines Volume 1, 7th Edition, 2015

2-56 CHAPTER 2 - Minimum Design Loads

For concrete or masonry shear wall buildings, it is also
permitted to use:

n a = 385 (C w ) os /h (207A.9-5)

where

ft = mean roof height (m)
n = number of shear walls in the building
effective in resisting lateral forces in the
direction under consideration
A b = base area of the structure (m 2 )

A = horizontal cross-section area of shear wall
“i” (m 2 )

p. = length of shear wall “i” (m)
hi ~ height of shear wall “i” (m)

207A.9.4 Rigid Buildings or Other Structures

For rigid buildings or other structures as defined in Section
207A.2, the gust-effect factor shall be taken as 0.85 01
calculated by the formula:

G =

0.925

rl + 1- 7g q/ z Q\
l l + 1.7g v / z )

In SI:

I- Z = c

(207A.9-6)

(207A.9-7)

where I? is the intensity of turbulence at height z

where z is the equivalent height of the structure defined as
0. 6/i, but not less than z mi „ for all building heights h. z min
and c are listed for each exposure in Table 207A.9-1; %q
and g v shall be taken as 3.4. The background response Q
is given by:

Q =

1 + 0. 63

(tt)

0.63

(207A.9-8)

where B and h are defined in Section 207 A.3 and L % is the
integral length scale of turbulence at the equivalent height
given by:

(207A.9-9)

In SI:

In which £ and e are constants listed in Table 207A.9-1.

207A.9.5 Flexible or Dynamically Sensitive Buildings
or Other Structures

For flexible or dynamically sensitive buildings or other
structures as defined in Section 207A.2, the gust-effect
factor shall be calculated by:

1 + 1. 71

= 0.925 !

(207A.9-10)

1 + 1. 7g v / z

gQ and g v shall be taken as 3.4 and g n is given by:

(207A.9-1 1)

g n = ,/21n(3600 n x )
0.577

+ -

72111 ( 3600 ^)

R, the resonant response factor, is given by:

-R n R h R B (0.53 + 0A7R L )

7. 47 Ni

n (1 + 10. 3 Ni ) 5 / 3

.. n i^2
N 1 = -T7—

(207A.9-12)

(207A.9-13)

(207A.9-14)

Association of Structural Engineers

of the Philippines. Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-57

= for ?7 > 0 (207A.9-15a)

n 277 2

R f = 1

for 77 = 0 (207A.9-15b)

w j iere the subscript € in Equation 207A.9-15 shall be taken
as ft. and ft, respectively, where ft, B , and ft are defined
in Section 207A.3.

fundamental natural frequency
R h setting rj = 4. 6n 1 ft/V 2r
setting 7] = 4- 6n t B/V^

R l setting 77 = 15.4nift/F z

damping ratio, percent of critical (i.e. for 2%

use 0.02 in the equation)

mean hourly wind speed (m/s) at height z

determined from Equation 207A.9-16:

<207A ' 9 • 1<i,

In SI:

where ft and a are constants listed in Table 207A.9-1 and
V is the basic wind speed in km/h.

207A.9.6 Rational Analysis

In lieu of the procedure defined in Sections 207A.9.3 and
207A.9.4, determination of the gust-effect factor by any
rational analysis defined in the recognized literature is
permitted.

207A.9.7 Limitations

Where combined gust-effect factors and pressure
coefficients (GC p ), (GC pi ), and ( GC p f ) are given in
figures and tables, the gust-effect factor shall not be
determined separately.

207A.10 Enclosure Classification

Commentary:

Accordingly , the code requires that a determination be
made of the amount of openings in the envelope to assess
enclosure classification ( enclosed , partially enclosed \ or
open), “ Openings " are specifically defined in this version
of the code as “ apertures or holes in the building envelope
which allow air to flow through the building envelope and
which are designed as “ open ” during design winds .
Examples include doors , operable windows, air intake
exhausts for air conditioning and or ventilation systems ,
gaps around doors, deliberate gaps in cladding, and
flexible and operable louvers . Once the enclosure
classification is known, the designer enters Table 207 A. 11 -
1 to select the appropriate internal pressure coefficient

This version of the code has four terms applicable to
enclosure: wind-borne debris regions, glazing, impact-
resistant glazing, and impact protective system. “Wind-
borne debris regions " are specified to alert the designer to
areas requiring consideration of missile impact design and
potential openings in the building envelope . " Glazing ” is
defined as “any glass or transparent or translucent plastic
sheet used in windows, doors, skylights, or curtain walls, "
“Impact resistant glazing >} is specifically defined as
“ glazing that has been shown by testing to withstand the
impact of test missiles . " “Impact protective systems'- over
glazing can be shutters or screens designed to withstand
wind-borne debris impact Impact resistance of glazing
and protective systems can be tested using the test method
specified in ASTM El 886-2005 (2005), with missiles,
impact speeds, and pass/fail criteria specified in ASTM
El 996-2009 (2009), Other approved test methods are
acceptable. Origins of missile impact provisions contained
in these standards are summarized in Minor (1994) and
Twisdale et al (1996): : •••.•

Attention is drawn to Section 2 07 A. 10.3, which requires
glazing in Category I, II, III , and IV buildings in wind-
borne debris regions to be protected with an impact
protective system or to be made of impact resistant glazing.
The option of unprotected glazing was eliminated for most
buildings in the 2005 edition of the standard to reduce the
amount of wind and water damage to buildings during
design wind storm events ,

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-58 CHAPTER 2 - Minimum Design Loads

Table 207A.9-1
Terrain Exposure Constants

Exposure

^(m)

€

Zmin(m)*

7.0

365.76

1/7

0.84

1/4.0

0.45

0.30

97.54

1/3.0

9.14

9.5

274.32

1/9.5

TOO

1/6.5

0.65

0.20

152.4

1/5.0

4.57

11.5

213.36

1/11.5

1.07

1/9.0

0.80

0.15

198.12

1/8.0

2.13

* z min - minimum height used to ensure that the equivalent height z is greater of 0.6/t or z min . For buildings with
h < z min , z shall be taken as z min .

Prior to the 2002 edition of the standard \ glazing in the
lower 18 m of Category IL HI, or IV buildings sited in
wind-borne debris regions was required to be protected
with an impact protective system, or to be made of
impact-resistant glazing , or the area of the glazing was
assumed to be open . Recognizing that glazing higher
than 18 m above grade may be broken by wind-borne
debris when a debris source is present, a new provision
was added in 2002 . With that new provision , aggregate
surfaced roofs on buildings within 450 m of the new
building need to be evaluated . For example, roof
aggregate, including gravel or stone used as ballast that
is not protected by a sufficiently high parapet should he
considered as a debris source. Accordingly , the glazing
in the new building, from 9 m above the source building
to grade would need to be protected with an impact
protective system or be made of impact-resistant
glazing. If loose roof aggregate is proposed for the new
building, it too should be considered as a debris source
because aggregate can be blown off the roof and be
propelled into glazing on the leeward side of the
building . Although other types of wind-borne debris can
impact glazing higher than IS m above grade, at these
higher elevations , loose roof aggregate has been the
predominate debris source in previous wind events. The
requirement for protection 9 m above the debris source
is to account for debris that can be lifted during flight.
The following references provide further information
regarding debris damage to glazing: Season et al.
(1984), Minor (1985 and 1994), Kareem (1986), and
Behr and Minor (1994).

Although wind-borne debris can occur in just about any
condition, the level of risk in comparison to the
postulated debris regions and impact criteria may also
be lower than that determined for the purpose of
standardization. For example, individual buildings may
he sited away from likely debris sources that would
generate significant risk of impacts similar in magnitude
to pea gravel (i.e., as simulated by 2 gram steel balls in
impact tests) or butt-on 2x4 impacts as required in
impact testing criteria. This situation describes a
condition of low vulnerability only as a result of limited
debris sources within the vicinity of the building. In

other cases , potential sources of debris may be present,
but extenuating conditions can lower the risk. These
extenuating conditions include the type of materials and
surrounding construction, the level of protection offered
by surrounding exposure conditions, and the design
wind speed. Therefore, the risk of impact may differ from
those postulated as a result of the conditions specifically
enumerated in the code and the referenced impact
standards. The committee recognizes that there are
vastly differing opinions , even within the standards
committee, regarding the significance of these
parameters that are not fully considered in developing
standardized debris regions or referenced impact
criteria.

Recognizing that the definition of the wind-borne debris
regions given in NS CP 2001 (ASCE 7-98) through
NSCP 2010 (ASCE 7-05) was largely based on
engineering judgment rather than a risk and reliability
analysis, the definition of the wind-borne debris regions
in ASCE 7-10 for Occupancy Category III and IV
buildings and structures has been chosen such that the
coastal areas included in the wind-borne debris regions
defined with the new wind speed maps are
approximately consistent with those given in the prior
editions for this risk category. Thus, the new wind speed
contours that define the wind-borne debris regions in
Section 207 A. 10.3.1 are not direct conversions of the
wind speed contours that are defined in NSCP 2010
(ASCE 7-05) as shown in Table C207A.5-6. As a result
of this shift, adjustments are needed to the Wind Zone
designations in ASTM E 1996 for the determination of
the appropriate missile size for the impact test because
the Wind Zones are based on the NSCP 2010 (ASCE 7-
05) wind speed maps. Chapter 6.2.2 of ASTM E 1996
should be as follows:

6.2.2 Unless otherwise specified ' select the wind
zone based on the basic wind speed as follows:

6.2.2. 1 Wind Zone 1-210 kph < basic wind speed <
225 kph.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2 - 59 .'

62X2 Wind Zone 2 - 225 kph < basic wind speed < 240
kph at greater than L6 km from the coastline . The
coastline shall be measured from the mean high water
.mark.

6,2X3 Wind Zone 3 - basic wind speed > 240 kph , or
basic wind speed > 225 kph and within 1.6 km of the
coastline . The coastline shall be measured from the
mean high water mark .

However , While the coastal areas included in the wind-
borne debris regions defined in the new wind speed
maps for Risk Category II are approximately consistent
with those given in NSCP2010 (ASCE 7-05), significant
reductions in the wind-borne debris regions for this risk
category occur in the area around Jacksonville, Florida ,
in the Florida Panhandle, and inland from the coast of
North Carolina .

The introduction of separate risk-based maps for
different risk categories provides a means for achieving
a more risk-consistent approach for defining wind-
borne debris regions. The approach selected was to link
the geographical definition of the wind-borne debris
regions to the wind speed contours in the maps that
correspond to the particular risk category . The resulting
expansion of the wind-borne debris region for
Occupancy Category I and II buildings and structures
(wind-borne debris regions in Figure 207 A, 5- 1 C that
are not part of the wind-borne debris regions defined in
Figure 207 A J- IB) was considered appropriate for the
types of buildings included in Occupancy Category I
and I L A review of the types of buildings and structures
currently included in Occupancy Category III suggests
that life safety issues would be most important, in the
expanded wind- borne debris region . for health care
facilities . Consequently , the committee chose to apply
the expanded wind-borne debris protection requirement
to this type of Occupancy Category III facilities and not
to all Occupancy Category III buildings and structures.

207A.10.1 General

For the purpose of determining internal pressure
coefficients, all buildings shall be classified as enclosed,
partially enclosed, or open as defined in Section 207A.2.

207A.10.2 Openings

A determination shall be made of the amount of openings
in the building envelope for use in determining the
enclosure classification.

207A.10.3 Protection of Glazed Openings

Glazed openings in Occupancy Category 1, II, III or IV
buildings located in tropical cyclone-prone regions shall be
protected as specified in this Section.

207A. 10.3.1 Wind-borne Debris Regions

Glazed openings shall be protected in accordance with
Section 207A. 10.3.2 in the following locations:

1. Within 1.6 km of the coastal mean high water line
where the basic wind speed is equal to or greater than
58 m/s, or

2. In areas where the basic wind speed is equal to or
greater than 63 ni/s.

For Occupancy Category 111 and IV buildings and
structures, except health care facilities, the wind-borne
debris region shall be based on Figure 207A.5-1A. For
Occupancy Category III health care facilities and
Occupancy Category II buildings and structures, the wind-
borne debris region shall be based on Figure 207A.5-1B.
Occupancy Categories shall be determined in accordance
with Section 103.

Exception:

Glazing located over IS m above the ground and over 9 m
above aggregate-surfaced- roofs, ineluding roofs with
gravel or stone ballast . located within 4x0 m of the
building shall be permuted to he unprotected.

207A.1 0.3.2 Protection Requirements for Glazed
Openings

Glazing in buildings requiring protection shall be protected
with an impact-protective system or shall be impact-
resistant glazing.

Impact-protective systems and impact-resistant glazing
shall be subjected to missile test and cyclic pressure
differential tests in accordance with ASTM El 996 as
applicable. Testing to demonstrate compliance with ASTM
El 996 shall be in accordance with ASTM El 886. Impact-
resistant glazing and impact protective systems shall
comply with the pass/fail criteria of Section 7 of ASTM
El 996 based on the missile required by Table 3 or Table 4
of ASTM El 996.

Exception:

National Structural Code of the Philippines Volume I, 7th Edition, 2015

0 CHAPTER 2 - Minimum Design Loads

izing and impact-protective systems in buildings and
ictures classified as Occupancy Category 1 in
ordance with Section 103 shall comply with the
hanced protection” requirements of Table 3 of ASTM
)96. Glazing and impact-protective systems in all other
ictures shall comply with the “basic protection”
uirements of Table 3 of ASTM El 996.

ser Note:

'w wind zones that are specified in ASTM El 996 for
>e in determining the applicable missile size for the
ipact test , have to be adjusted for use with the wind
>eed maps of this code and the corresponding wind-
vne debris regions , see Section C207A. 10.3.2.

?A.l(h4 Multiple Classifications

i building by definition complies with both the “open”

1 “partially enclosed” definitions, it shall be classified as
“open” building. A building that does not comply with
ler the “open” or “partially enclosed” definitions shall
classified as an “enclosed” building.

7A.11 Internal Pressure Coefficient

mmentaiy:

? internal pressure coefficient values in
hie 2 07 A. 11-1 were obtained from wind tunnel tests
athopoidos et al. 1979) and full-scale data (Yea t Is and
hta 1993). Even though the wind tunnel tests were
uiucted primarily for low-rise buildings , the internal
'ssure coefficient values are assumed to be valid for
idings of any height . The values (GC pi ) = +0.1$ and
IS are for enclosed buildings. It is assumed that the
'I ding has no dominant opening or openings and that the
all leakage paths that do exist are essentially uniformly
tributed over the buildings envelope . The internal
? ssure coefficient values for partially enclosed buildings
lime that the building has a dominant opening or
?nings. For such a building, the internal pressure is
kited by the exterior pressure at the opening and is
ically increased substantially as a result , Net loads, that
the combination of the internal and exterior pressures,

? therefore also significantly increased on the building
faces that do not contain the opening . Therefore, higher
Cpj) values of +0.55 and -0.55 are applicable to this
ie. These values include a reduction factor to account
■ the lack of perfect correlation between the internal
assure and the external pressures on the building
faces not containing the opening (Invin 1987 and Beste
d Cermak 1996). Taken in isolation, the internal

pressure coefficients can reach values of ±0.8 (or possibly
even higher on the negative side).

For partially enclosed buildings containing a large
unpartitioned space, the response time of the internal
pressure is increased, and this increase reduces the ability
of the internal pressure to respond to rapid changes in
pressure at an opening. The gust factor applicable to the
internal pressure is therefore reduced. Equation 207 A. IF
1, which is based on Vickeiy and Bloxham (1992) and
Irwin and Dunn (1994), is provided as a means of adjusting
the gust factor for this effect on structures with large
internal spaces, such as stadiums and arenas.

Because of the nature of tropical cyclone winds and
exposure to debris hazards (Minor and Behr 1993), glazing
located below IS m above the ground level of buildings
sited in wind- borne debris regions has a widely varying
and comparatively higher vulnerability to breakage from
missiles, unless the glazing can withstand reasonable
missile loads and subsequent wind loading, or the glazing
is protected by suitable shutters. (See Section C207AJ0for
discussion of glazing above 18 m. When glazing is
breached by missiles, development of higher internal
pressure may result, which can overload the cladding or
structure if the higher pressure was not accounted for in
the design. Breaching of glazing can also result in a
significant amount of water infiltration, which typically
results in considerable damage to the building and its
contents (Surry et al. 1977, Reinhold 1982, and Stubbs and
Perry 1993).

The influence of compartmentalization on the distribution
of increased internal pressure has not been researched. If
the space behind breached glazing is separated from the
remainder of the building by a sufficiently strong and
reasonably airtight compartment, the increased internal
pressure would likely be confined to that compartment.
However, if the compartment is breached (e.g., by an open
corridor door or by collapse of the compartment wall), the
increased internal pressure will spread beyond the initial
compartment quite rapidly. The next compartment may
contain the higher pressure, or it too could be breached,
thereby allowing the high internal pressure to continue to
propagate. Because of the great amount of air leakage that
often occurs at large hangar doors, designers of hangars
should consider utilizing the internal pressure coefficients
for partially enclosed buildings in Table 207 A. 1 1-1.

207A.11.1 Internal Pressure Coefficients

Internal pressure coefficients, (GC pi ), shall be determined
from Table 207A.U-1 based on building enclosure
classifications determined from Section 207 A. 1 0.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAP i ER 2 - Minimum Design Loads 2-61

Table 207A.11-1

Internal Pressure Coefficient, (GC pi )

Main Wind Force Resisting
System and Components and
Cladding

All Heights

"^Enclosed, Partially Enclosed, and
Open Buildings

Walls & Roofs

Enclosure Classification

(GC pi )

Open Buildings

0.00

Partially Enclosed Buildings

+0.55

-0.55

Enclosed Buildings

+0.18

-0.18

Notes:

1. Plus and minus signs signify pressures acting toward
and away from the internal surfaces, respectively.

2. Values of ( GC pi ) shall be used with q z or q h as
specified.

3. Two cases shall be considered to determine the critical
load requirements for the appropriate condition:

L a positive value of (GC p i) applied to all internal
surfaces

ii. a negative value of ( GC pi ) applied to all
internal surfaces

207 A.1 1.1.1 Reduction Factor for Large Volume
Buildings, R t

For a partially enclosed building containing a single,
unpartitioned large volume, the internal pressure
coefficient, (GC pi ), shall be multiplied by the following
reduction factor,

Ri — 1.0 or

= 0.5

1 +■

1 +

7 A

< 1.0 (207 A. 1 1-1)

°g /

where

^og

total area of openings in the building
envelope (walls and roof), in m 2
unpartitioned internal volume, in m 3

207B Wind Loads On Buildings — MWFRS

(Directional Procedure)

Commentary:

The Direct ional Procedure is the former ° buildings of all
heights' 1 provision in Method 2 of NSCP 2010 (ASCE 7-
05) for MWFRS. A simplified method based on this
Directional Procedure is provided for buildings up to 49 m
in height . The Directional Procedure is considered the
traditional approach in that the pressure coefficients
reflect the actual loading on each surface of the building
as a function of wind direction , namely t winds
perpendicular or parallel to the ridge line .

207B.1 Scope

207B.1.1 Building Types

This chapter applies to the determination of MWFRS wind
loads on enclosed, partially enclosed, and open buildings
of all heights using the Directional Procedure.

L Part 1 applies to buildings of all heights where it is
necessary to separate applied wind loads onto the
windward, leeward, and side walls of the building to
properly assess the internal forces in the MWFRS
members.

2. Part 2 applies to a special class of buildings designated
as enclosed simple diaphragm buildings, as defined in
Section 207A.2, with h < 48 m.

207B.1.2 Conditions

A building whose design wind loads are determined in
accordance with this chapter shall comply with all of the
following conditions:

1 . The building is a regular-shaped building or structure
as defined in Section 207A.2.

2. The building does not have response characteristics
making it subject to across-wind loading, vortex
shedding, instability due to galloping or flutter; or it
does not have a site location for which channeling
effects or buffeting in the wake of upwind obstructions
warrant special consideration.

National Structural Code of the Philippines Volume L 7th Edition, 2015

2-62 CHAPTER 2 - Minimum Design Loads

207B.1.3 Limitations

The provisions of this chapter take into consideration the
load magnification effect caused by gusts in resonance with
along-wind vibrations of flexible buildings. Buildings not
meeting the requirements of Section 207B.1.2, or having
unusual shapes or response characteristics shall be
designed using recognized literature documenting such
wind load effects or shall use the wind tunnel procedure
specified in Section 207F.

207B.L4 Shielding

There shall be no reductions in velocity pressure due to
apparent shielding afforded by buildings and other
structures or terrain features.

Part 1: Enclosed, Partially Enclosed, and Open
Buildings of AH Heights

207B.2 General Requirements

The steps to determine the wind loads on the MWFRS for
enclosed, partially enclosed and open buildings of all
heights are provided in Table 207B.2-1 .

User Note:

Use Part 1 of Section 207 B to determine wind pressures
on the MWFRS of enclosed, partially enclosed or an
open building with any general plan shape \ building
height or roof geometry that matches the figures
provided . These provisions utilize the traditional " all
heights ” method (Directional Procedure) by calculating
wind pressures using specific wind pressure equations
applicable to each building surface .

207BJL1 Wind Load Parameters Specified in Section
207A

The following wind load parameters shall be determined in
accordance with Section 207A:

• Basic Wind Speed, V (Section 207A.5)

(Section 207A.1 1)

207B.3 Velocity Pressure

207B.3.1 Velocity Pressure Exposure Coefficient

Based on the exposure category determined in Section
207A.7.3, a velocity pressure exposure coefficient K z or
K h , as applicable, shall be determined from Table 207B.3-
L For a site located in a transition zone between exposure
categories that is near to a change in ground surface
roughness, intermediate values of K z or K /t , between those
shown in Table 207B.3-1 are permitted provided that they
are determined by a rational analysis method defined in the
recognized literature.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-63

Table 207B.2-1

Steps to Determine MWFRS Wind
Loads for Enclosed, Partially Enclosed and Open
Buildings of All Heights

'■

BMW'S

lllllll il:;;

Step 1: Determine risk category of building or other
structure, see Table 103-1

Step 2: Determine the basic wind speed, F, for the
applicable risk category, see Figure 207A.5-
| , 1A, BorC

Step 3: Determine wind load parameters:

> Wind directionality factor, K d , see
Section 207 A. 6 and Table 207 A. 6-1

> Exposure category, see Section 207A.7

> Topographic factor, K zt , see
Section 207A.S and Table 207A.8-1

> Gust Effect Factor, G , see Section 207A.9

> Enclosure classification, see
Section 207A.10

> Internal pressure coefficient, ( GC pi ), see
Section 207A. 1 1 and Table 207A. 11-1

Determine velocity pressure exposure
coefficient, K z or K /n see Table 207B.3-1

Step 4:

Step 5:

Step 6:

Step 7:

Determine velocity
Equation 207B.3-1

pressure q 7 or q h

Determine external pressure coefficient, C p or

C N

> Figure 207B.4-1 for walls and flat, gable,
hip, monoslope or mansard roofs

> Figure 207B.4-2 for domed roofs

> Figure 207B.4-3 for arched roofs

> Figure 207B.4-4 for monoslope roof,
open building

> Figure 207B,4-5 for pitched roof, open
building

> Figure 207B.4-6 for troughed roof, open
building

> Figure 207B.4-7 for along-ridge/valley
wind load case for monoslope, pitched or
troughed roof, open building

Calculate wind pressure, p, on each building

surface

> Equation 207B.4-1 for rigid buildings

> Equation 207B.4-2 for flexible buildings

> Equation 207B.4-3 for open buildings

Commentary:

The velocity pressure exposure coefficient K z can be
obtained using the equation:

, z

2.01 —

2/a

For 4.57m < (C207B.

Z<Zc

2,01

4. 57

2 /

Forz < 4.57 m

3-1)

(C207B.

3-2)

in which values of a and z g are given in Table 207A.9-1.
These equations are now given in Tables 207 B 3-1,
207C3-1, 20703-1 and207E.3-l to aid the user .

Changes were implemented in NSCP 2001 (ASCE 7-98),
including truncation of K z values for Exposures A and B
below heights of 30 m and 9 m, respectively , applicable to
Components and Cladding and the Envelope Procedure .
Exposure A was eliminated in the 2002 edition of ASCE 7.

In the NSCP 2010 (ASCE 7-05) standard , the K z
expressions were unchanged from NSCP 2001 (ASCE 7-
98). However, the possibility of interpolating between the
standard exposures using a rational method was added in
the NSCP 2010 (ASCE 7-05) edition. One rational method
is provided in the following text.

To a reasonable approximation , the empirical exponent a
and gradient height z g in the preceding expressions
(Equations C207B3-1 and C207B3-2) for exposure
coefficient K z may be related to the roughness length z 0
(where z 0 is defined in Section 0207 A .7) by the relations

a = c t z 0

- 0.133

and

where

z g~ C 2 z O

0.125

(C207B3-3)

(C207B3-4)

Units of z 0 , z g

5.65

c 2

450

■

mmy:

into

The preceding relationships are based on matching the
ESDU boundary layer model (Harris and Deaves 1981 and
ESDU 1990 and 1993) empirically with the power law
relationship in Equations C207B3-1 and C207B3-2, the
ESDU model being applied at latitude 35° with a gradient

National Structural Code of the Philippines Volume 1, 7th Edition, 2015

2-64 CHAPTER 2 - Minimum Design Loads

wind of 75 m/s . If z 0 has been determined for a particular
upwind fetch , Equations C2Q7B3-1 through C207B.3-4
can be used to evaluate K z . The correspondence between
z 0 and the parameters a and z„ implied by these
relationships does not align exactly with that described in
the commentary to ASCE 7-95 and 7-9S. However ; the
differences are relatively small and not of practical
consequence* The ESDU boundary layer model has also
been used to derive the following simplified method (Irwin
2006) of evaluating K z following a transition from one
surface roughness to another. For more precise estimates
the reader is referred to the original ESDU model (Harris
and Deaves 1981 and ESDU 1990 and 1993).

In uniform terrain the wind travels a sufficient distance
over the terrain for the planetary boundary layer to reach
an equilibrium state . The exposure coefficient values in
Table 207B.3-1 are intended for this condition . Suppose
that the site is a distance x miles downwind of a change in
terrain : The equilibrium value of the exposure coefficient
at height z for the terrain roughness downwind of the
change will be denoted by K zd> and the equilibrium value
for the terrain roughness upwind of the change will be
denoted by K zw The effect of the change in terrain
roughness on the exposure coefficient at the site can be
represented by adjusting K zd by an increment AK, thus
arriving at a corrected value K z for the site .

K z = K zd T AK (C207B.3-5)

In this expression AK is calculated using:

AK = (K 33 , u - K 334 ) Ell. Fak ( x ) (C207B.3-6)

\AK\ < | K zu - K zd |

where K 33d and K 33u are respectively the downwind and
upwind equilibrium values of exposure coefficient at 10 m
height , and the function F AK (x) is given by:

FjucW = log 10 @ /log 10 (^) (C207B.3-7)

For x 0 < x < x x

F ak {x) = 1 forxCXo

Fak( x )

0 for x > x t

In the preceding relationships

Xq = C 3 XlO"( ,f 33,‘|-^33.u) -2-3

(C207B.3-8). |

The constant c 3 = 1.0 km. The length x t = 10 km Jbfgi
K 334 < K 33 u (wind going from smoother terrain upwinM
to rougher terrain downwind) or X\ = 100 km) for K 334 yy
K 33u (wind going front rougher terrain upwind toff
smoother terrain downwind).

The above description is in terms of a single roughnes . |J
change. The method can be extended to multiple roughness f
changes. The extension of the method is best described byfi
an example. Figure C207B.3-1 shows wind with an initial j§
profile characteristic of Exposure D encountering anK
expanse ofB roughness, followed by a further expanse q|j|
D roughness and then some more B roughness agaidjf)
before it arrives at the building site. This situation «||
representative of wind from the sea flowing over an outer §|
strip of land, then a coastal waterway, and then some J|
suburban roughness before arriving at the building site, ft.
The above method for a single roughness change is first
used to compute the profile of K z at station l in 1" igure
C207B.3-L Call this profile K { z \ The value of AK for the |
transition between stations l and 2 is then determined |
using the equilibrium value of K 33u for the roughness |
immediately upwind of station /, /. as though the |
roughness upwind of station l extended to infinity . ThiSf
value of AK is then added to the equilibrium value K\ ' of\
the exposure coefficient for the roughness between stations J
1 and 2 to obtain the profile of K 7 at station 2, which we >
will call K^\ Note however, that the value of K^ z ] in this \
way cannot be any lower than K z l \ The process is then :
repeated for the transition between stations 2 and 3. Thus , '
AK for the transition from station 2 to station 3 is
calculated using the value of K 33 u for the equilibrium
profile of the roughness immediately upwind of station 2, y
and the value of K 33>d for the equilibrium profile of the |
roughness downwind of station 2 . This value of AK is then
added to ft^ 2) to obtain the profile K^ at station 3, with
the limitation that the value of cannot be any higher
than K^\

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAP ! ER 2 •“ Minimum Design Loads 2-65

“W"

_jijnrbnTui_

^njinjirJ InjiiinruTimrui

Roughness Roughness Roughness

||§'©-" 0 B OB

Figure C207B.3-1

^||||fe^ Multiple Roughness Changes Due to
Coastal Waterway

Mp;-;

/. s/>?e/e roughness change: Suppose the building

for //><? open ter rain

11111= CtZo " 0133 = 6.62

XO. 066-° 133

z 0 =
and

= 9.5

0 125

1,273

XO. 066° 125

= 275 /«

applying Equation C 207 B. 3-1 at 20 m and 10

mm^hetghis.

K zu = 2

/ 66 \
01 \906/

2/9.5

l< 33 , „ = 2.01

(— )

\906/

2/9.5

= 1.16 and

= /.0

pSp:'

|||Sj§ Similarly, for the suburban terrain

“©fafcjZo- 0 - 133 = 6. 62x1. 0~° 133

llrs//:-

= 6.62

^-c 2 z 0 0125 = 1,2 73x1.0° 125 = 388 m

l|g | therefore

m?A \

Wim

, 66 x 2/619

K zll = 2.01 — —
'1,273/

33 \ 2 7 662

= 0.77 and

201 y

gg|.|#r<wi Equation C207B.3-S

x o = C 3 X 10 - ^ 33d- ^ 33 .“) 2-2 ' 3

= 0.57

■ . ; v

lii©!©;'.-

= o.62ixio-(° 62 - 100)2 - 23

= 0.00241 mi

From Equation C207B.3-7

/ 6 . 21 \ / / 6.21 \

“ ,0gl ° (o.36// 10§10 (o.0024l) = ° 36

Therefore from Equation C207B.3-6

0. 82

dtf = (1. 00 - 0. 67) 0. 36 = 0. 15

Note that because \AK\ is 0.15, which is less than the 0.3S
value of\K 33n ~~ K^ id \, 0.15 is retained. Finally , from
Equation C207B.3-5 , the value ofK z is:

K z = K zd + AK = 0.82 + 0. 15 = 0. 97

Because the value 0.97 for K z lies between the values 0.SS
and 1.16, which would be derived from Table 207 B. 3-1 for
Exposures B and C respectively, it is an acceptable
interpolation. If it falls below the Exposure B value , then
the Exposure B value of K z is to be used. The value K z »
0.97 may be compared with the value LI 6 that would be
required by the simple 792 m fetch length requirement of
Section 207A.7.3.

The most common case o f a single roughness change where
an interpolated value of K z is needed is for the transition
from Exposure C to Exposure B, as in the example just
described. For this particular transition, using the typical
values of Zq of 0.02 m and 0.3 m, the preceding formulae
can be simplified to:

K z = ( 1 -I- 0. 146 log jo (fff (C207B.3-9)

I< zB <K z < K zC

where x is in miles , and K zd is computed using a = 6.62.
K 2B and K zC are the exposure coefficients in the standard
Exposures C and B, Figure C 207 B. 3-2 illustrates the
transition from terrain roughness C to terrain roughness B
from this expression. Note that it is acceptable to use the
typical z 0 rather than the lower limit for Exposure B in
deriving this formula because the rate of transition of the
wind profiles is dependent on average roughness over
significant distances , not local roughness anomalies. The
potential effects of local roughness anomalies , such as

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-66 CHAPTER 2 - Minimum Design Loads

parking lots and playing fields, are covered by using the
standard Exposure B value of exposure coefficient, K 2B , as

Example 2j Multiple Roughness Change Suppose we have
a coastal waterway situation as illustrated in Figure
C207B.3-1, where the wind comes from open sea with
roughness type D, for which we assume z 0 = 0. 003 m,
and passes over a strip of land 1.61 km wide, which is
covered in buildings that produce typical B type roughness,
i.e. z 0 = 0. 3 m . It then passes over a 3.22-km wide strip
of coastal waterway where the roughness is again
characterized by the open water value z 0 = 0. 003 m. It
then travels over 0.16 km of roughness type B (z 0 = 0.3 m
before arriving at the site, station 3 in Figure C207B.3-1,

where the exposure coefficient is required at the IS- fiL.
height. The exposure coefficient at station 3 at 15 m heightf
is calculated as shown in Table C207B.3-1 .

■

The value of the exposure coefficient at 15 m at station 3 iff
seen from the table to be 1.067 . This is above that fdff
Exposure B, which would be 0.81, but well below that fd$$
Exposure D, which would be 1.27, and similar to that fa jfp
Exposure C, which would be 1.09.

EXP. C, x = 0 km *

x - 0.08 km

x - 0.32 km

x — 0.80 km

x = 1.60 km

EXP. 8

Figure C 2 07 B. 3-2

Transition from Terrain Roughness C to Terrain Roughness B, Equation C207B. 3.1-9

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-67

Table C207B.3-1
Tabulated Exposure Coefficients

Transition from sea to station 1

K to, «

1.215

K 104

0.667

K 15, d
0.755

f ak

0.220

ak 15

0.137

K m

l\ 7

0.8 95

Transition from sea to station 2

1^10, u

K lO.d

fi'is.d

AKi 5

0.667

L215

1.215

0.324

- 0.190

1.111

Transition from sea to station 3

K io*

K 10, d

K l 5 , d

Fak

AKis

4 3)

1.215

0.667

0.498

0.310

1.067

Note: The equilibrium values of the exposure coefficients , K t0u , K 10d and K tsd (downwind value of K z at 15 m), were
calculated from Equation C2Q7B-1 using a and z g values obtained from Equations C207B-3 and C207B-4 with the
roughness values given. Then F^ K is calculated using Equations C207B-7 and C207B-8, and then the value of AK at 15 m
height , AK 1S , is calculated from Equation C207B-6 . Finally , the exposure coefficient at 15 in at station i, is obtained
(from Equation C207B-5.

207B.3.2 Velocity Pressure

Velocity pressure, q z , evaluated at height z shall be
calculated by the following equation:

q z = 0. 613K z K zt I< d V 2 (Wm 2 )\V in m/s (207B.3-1)

where

K d =

wind directionality factor, see

Section 207A.6

K* =

velocity pressure exposure coefficient, see
Section 207B.3.1

topographic factor defined, see

Section 207A.8.2

basic wind speed, see Section 207A.5

Qz =

velocity pressure calculated using
Equation 207B.3-1 at height z

Qzt ~

velocity pressure calculated using
Equation 207B.3-1 at mean roof height h

The numerical coefficient 0.613 shall be used except where
sufficient climatic data are available to justify the selection
of a different value of this coefficient for a design
application.

Commentary:

The basic wind speed is converted to a velocity pressure
q 7 in (N/m 2 ) at height z by the use of Equation 2Q7B.3-

L •••• • ••• . • '

The constant 0.613 refects the mass density of air for
the standard atmosphere , that is t temperature of 15 °C
and sea level pressure of 101:325 kPa t and dimensions
associated with wind speed in m/s * The constant is
obtained as follows:

constant - 1/2[(1.225 kg/m 2 )f (9. 81 m/s 2 )] *

[(m/s)] 2 [9.81 N/kg]

- 0.613

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-68 CHAPTER 2 - Minimum Design Loads

207B.4 Wind Loads — Main Wind Force-Resisting
System

207B.4.1 Enclosed and Partially Enclosed Rigid
Buildings

Design wind pressures for the MWFRS of buildings of all
heights shall be determined by the following equation:

p = qGC p - qi(GC pi ) (N/m 2 ) (207B.4-1)

where

c v

(GC pi )

q z for windward walls evaluated at

height z above the ground

qi t for leeward walls, side walls, and

roofs, evaluated at height h

q h for windward walls, side walls,

leeward walls, and roofs of enclosed

buildings and for negative internal

pressure evaluation in partially enclosed

buildings

q z for positive internal pressure
evaluation in partially enclosed buildings
where height z is defined as the level of
the highest opening in the building that
could affect the positive internal
pressure. For buildings sited in wind-
borne debris regions, glazing that is not
impact resistant or protected with an
impact resistant covering shall be treated
as an opening in accordance with Section
207A.10.3. "

For positive internal pressure evaluation,
q t may conservatively be evaluated at
height h(q t ~ q h )

gust-effect factor, see Section 207A.9
external pressure coefficient from
Figures 207B.4-1, 207B.4-2 and 207B.4-
3

internal pressure coefficient from
Table 207AT1-1

q and q t shall be evaluated using exposure defined in
Section 207A.7.3. Pressure shall be applied simultaneously
on windward and leeward walls and on roof surfaces as
defined in Figures 207B.4-1, 207B.4-2 and 207B.4-3.

The numerical constant of 0.613 should be used except
where sufficient weather data are available to justify a
different value of this constant for a specific design
application. The mass density of air will vary as a function
of altitude, latitude, temperature, weather, and season.
Average and extreme values of air density are given in
Table C207B.3-2.

Table 207B.3-1

Velocity Pressure Exposure Coefficients, K h and I( z
Main Wind Force Resisting System - Part 1

Height above
ground level, z

Exposure

(m)

i/\

057

0.85

1.03

6.0

0.62

0.90

1.08

7.5

0.66

0.94

1.12

9.0

0.70

0.98

1.16

12.0

0.76

1.04

1.22

15.0

0.81

1.09

1.27

18.0

0.85

1.13

1.31

21.0

0.89

1.17

1.34

24.0

0.93

1.21

1.38

27.0

0.96

1.24

1.40

30.0

0.99

1.26

1.43

36.0

1.04

1.31

1.48

42.0

1.09

1.36

1.52

48.0

1.13

1.39

1.55

54.0

1.17

1.43

1.58

60.0

1.20

1.46

1.61

75.0

1.28

1.53

1.68

90.0

1.35

1.59

1.73

105.0

1.41

1.64

1.78

120.0

1.47

1.69

1.82

135.0

1.52

1.73

1.86

150.0

1.56

1.77

1.89

Notes:

1 . The velocity pressure exposure coefficient K z , may be
determined from the following formula:

For 4.5 m < z < z g For z < 4.5 m

I< 7 = 2. Ol(z/z g ) 2/ “ Ky = 2. 01(4. 5 /z g ) 2/ "

2. a and z g are tabulated in Table 207A.9. 1 .

3. Linear interpolation for intermediate values of height
z is acceptable.

4. Exposure categories are defined Section 207A.7.
Commentary :

Loads on Main Wind-Force Resisting Systems: In
Equations 2Q7B.4-1 and 207BA-2 , a velocity pressure
term qi appears that is defined as the *' velocity pressure
for internal pressure determination . ” The positive
internal pressure is dictated by the positive exterior
pressure on the windward face at the point where there
is an opening . The positive exterior pressure at the
opening is governed by the value of q at the level of the

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2~69

fffpening, not <\\ v For positive internal pressure
I evaluation , qi may conservatively be evaluated at height
h(q i = q h ). For low buildings this does not make much
difference, but for the example of a 90-m tall building in
Exposure B with a highest opening at 18 m, the
^difference between q 90 and q 1Q represents a 59 percent
idherease in internal pressure . This difference is
unrealistic and represents an unnecessaty degree of
fppmervatism. Accordingly, q t = q h for positive
f internal pressure evaluation in partially enclosed
fffuildings where height z is defined as the level of the
1 Highest opening in the building that could affect the
positive internal pressure , For buildings sited in wind -
f borne debris regions, with glazing that is not impact
% resistant or protected with an impact protective system,
should be treated on the assumption there will be an
opening.

Figure 207 B. 4-1. The pressure coefficients for
MWFRSs are separated into two categories:

|p! Directional Procedure for buildings of all heights
fp (Figure 207BA-1) as specified in Section 207Bfor
Jj buildings meeting the requirements specified
' therein.

Envelope Procedure for low-rise buildings having
fi a height less than or equal to IS m (Figure 207C.4-
l§|§, 1) as specified in Section 207C for buildings
3! meeting the requirements specified therein.

fin generating these coefficients, two distinctly different
(approaches were used. For the pressure coefficients
(given in Figure 207 B. 4-1, the more traditional approach
f$f m followed and the pressure coefficients reflect the
actual loading on each surface of the building as a
function of wind direction; namely, winds perpendicular
or parallel to the ridge line . Observations in wind tunnel
(tests show that areas of very low negative pressure and
(even: slightly positive pressure can occur in all roof
(structures, particularly as the distance from the
Windward edge increases and the wind streams reattach
fid: the surface. These pressures can occur even for
t relatively flat or low slope roof structures. Experience

and judgment from wind tunnel studies have been used
to specify either zero or slightly negative pressures
(-0.18) depending on the negative pressure coefficient.
These values require the designer to consider a zero or
slightly positive net wind pressure in the load
combinations of Section 203.

Table C207B.3-2

Ambient Air Density Values for Various Altitudes

Altitude

Ambient Air Temperature

Meters

Minimum

Average

Maximum

(kg/m 3 )

1.1392

1.2240

1.3152

305

1.1 088

1.1872

1.2720

610

1.0800

1.1520

L2288

914

1.0512

1.1184

1.1888

WOO

1.0432

1.1088

1.1776

1219

1.0240

1.0848

1.1488

1524

0.9984

1.0544

1.1120

1829

0.9728

1.0224

1.0752

2000

0.9584

1.0064

1.0560

2134

0.9472

0.9920

1.0400

2438

0.9232

0.9632

1.0048

2743

0.8976

0.9344

0.9712

3000

0.8784

0.9104

0.9456

3048

0.S752

0.9072

0.9408

National Structural Code of the Philippines Volume L 7th Edition, 2015

2-70 CHAP i ER 2 - Minimum Design Loads

Figure C207B.4-1

Application of Minimum Wind Load

Figure 207 B. 4-2. Frame loads on dome roofs are adapted
from the Eurocode (1995). The loads are based on data
obtained in a modeled atmospheric boundary-layer flow
that does not fully comply with requirements for wind-
tunnel testing specified in this code (Blessman 1971).
Loads for three domes ( h D /0 = O.S,f/D = O.S),(h D /
D = 0, f/D = 0.5), and ( hD/D = 0 J/D = 0.33) are
roughly consistent with data of Taylor (1991), who used an
atmospheric boundaty layer as required in this code . Two
load cases are defined \ one of which has a linear variation
of pressure from A to B as in the Eurocode (1995) and one
in which the pressure at A is held constant from 0° to 25°;
these two cases are based on comparison of the Eurocode
provisions with Taylor (1991). Case A (the Eurocode
calculation) is necessary in many cases to define maximum
uplift. Case B is necessaiy to properly define positive
pressures for some cases , which cannot be isolated with
current information , and which result in maximum base
shear. For domes larger than 60 m in diameter the
designer should consider use of wind-tunnel testing.
Resonant response is not considered in these provisions.
Wind-tunnel testing should be used to consider resonant
response. Local bending moments in the dome shell may be
larger than predicted by this method due to the difference
between instantaneous local pressure distributions and
those predicted by Figure 207 B. 4-2. If the dome is
supported on vertical walls directly below \ it is appropriate
to consider the walls as a “ chimney ” using Figure 207D. 5-
1 .

Figure 207B.4-3 . The pressure and force coefficient values
in these tables are unchanged from ANSI A58.1-1972. The
coefficients specified in these tables are based on wind-
tunnel tests conducted under conditions of uniform flow
and low turbulence t and their validity in turbulent
boundary-layer flows has yet to be completely established.
Additional pressure coefficients for conditions not
specified herein may be found in SI A (1956) and ASCE
(1961).

207B.4.2 Enclosed and Partially Enclosed Flexible
Buildings

Design wind pressures for the MWFRS of flexible
buildings shall be determined from the following equation:

p = qGfCp - q t (GC pl ) (N/m 2 ) (207B.4-2)

where q, q h C p , and (GC pi ) are as defined in Section
207B.4.1 and Gf (gust-effect factor) is determined in
accordance with Section 207A.9.5.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-71

?07B.4.3 Open Buildings with Monoslope, Pitched, or
Troughed Free Roofs

The net design pressure for the MWFRS of open buildings
with monoslope, pitched, or troughed roofs shall be
determined by the following equation:

P = <!hGC N (N/m 2 ) (207B.4-3)

where

|. q h “ velocity pressure evaluated at mean roof
height h using the exposure as defined in
Section 207A.7.3 that results in the highest
wind loads for any wind direction at the
site

G ~ gust-effect factor from Section 207A.9
C N = net pressure coefficient determined from
Figures 207 B. 4-4 through 207 B, 4-7

Net pressure coefficients, C N , include contributions from
top and bottom surfaces. Ail load cases shown for each roof
angle shall be investigated. Plus and minus signs signify
pressure acting toward and away from the top surface of
the roof, respectively.

For free roofs with an angle of plane of roof from
horizontal 0 less than or equal to 5° and containing fascia
panels, the fascia panel shall be considered an inverted
parapet. The contribution of loads on the fascia to the
MWFRS loads shall be determined using Section 207B.4.5
with q p equal to q h .

| Commentary:

Figures 2078,4-4 through 2078. 4-6 and 207E.8-1
through 207E.8-3 are presented for wind loads on
MWFRSs and components and cladding of open
buildings with roofs as shown, respectively. This work is
based on the Australian Standard AS 1 170.2-2000, Part
v2: Wind Actions, with modifications to the MWFRS
pressure coefficients based on recent studies (Altman
• | W(id Uematsu and Stathopoulos 2003).

Two load cases, A and 8, are given in Figures 207B. 4-4
through 2078.4-6. These pressure distributions provide
loads that envelop the results from detailed wind-tunnel
measurements of simultaneous normal forces and
moments. Application of both load cases is required to
\ envelop the combinations of maximum normal forces
and moments that are appropriate for the particular
l roof shape and blockage configuration.

■ The roof wind loading on open building roofs is highly
dependent upon whether goods or materials are stored

under the roof and restrict the wind flow. Restricting the
flow can introduce substantial upward acting pressures
on the bottom surface of the roof thus increasing (hex
resultant uplift load on the roof. Figures 2078.4-4
through 2078.4-6 and 207E.8- 1 through 207E.8-3 offer
the designer two options. Option 1 (clear wind flow)
implies little (less than 50 percent) or no portion of the
cross-section below the roof is blocked. Option 2
(obstructed wind flow) implies that a significant portion
(more them 75 percent is typically referenced in the
literature) of the cross-section is blocked by goods or
materials below the roof Clearly, values would change
from one set of coefficients to the other following some
sort of smooth , but as yet unknown, relationship , In
developing the provisions included in this code , the
50 percent blockage value was selected for Option 1,
with the expectation that it represents a somewhat
conservative transition. If the designer is not clear about
usage of the space below the roof or if the usage could
change to restrict free airflow , then design loads for
both options should be used.

207R.4.4 Roof Overhangs

The positive external pressure on the bottom surface of
windward roof overhangs shall be determined using
C p ss 0.8 and combined with the top surface pressures
determined using Figure 207B.4-1.

207B.4.5 Parapets

The design wind pressure for the effect of parapets on
MWFRS of rigid or flexible buildings with flat, gable, or
hip roofs shall be determined by the following equation:

P p = <l P (GC pn ) (N/m 2 ) 207B.4-4

where

p p = combined net pressure on the parapet due
to the combination of the net pressures
from the front and back parapet surfaces.
Plus (and minus) signs signify net
pressure acting toward (and away from)
the front (exterior) side of the parapet
q p = velocity pressure evaluated at the top of
the parapet

combined net pressure coefficient
-H .5 for windward parapet
-1.0 for leeward parapet

(cc p „)

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-72 CHAPTER 2 - Minimum Design Loads

207B.4.6 Design Wind Load Cases

The MWFRS of buildings of all heights, whose wind loads
have been determined under the provisions of this chapter,
shall be designed for the wind load cases as defined in
Figure 207B.4-8.

Exception;

Buildings meeting the requirements of Section DJ.J of
Appendix D, ASCE 7-10 need only he designed for Case 1
and Case 3 of Figure 207 B. 4-8.

The eccentricity e for rigid structures shall be measured
from the geometric center of the building face and shall be
considered for each principal axis (e x ,e Y ). The
eccentricity e for flexible structures shall be determined
from the following equation and shall be considered for
each principal axis ( e x , ey)-

e Q + l-71/ 2 .

(g QQ e Q) + (0/t Re /t) 2

!-• 71I 2 J(g Q Qe Q j + (BnRef) 2

207 B. 4-5

where

e Q = eccentricity e as determined for rigid
structures in Figure 207B.4-S
e R = distance between the elastic shear center
and center of mass of each floor
h* g <?7 (?> and R shall be as defined in Section
207A.9

The sign of the eccentricity e shall be plus or minus,
whichever causes the more severe load effect.

Commentary:

Wind tunnel research (Isyumov 1983, Boggs et ai 2000 \
kyumov and Case 2000, and Xie and Irwin 2000) has
shown that torsional load is caused by non-uniform
pressure on the different faces of the building from wind
flow around the building , interference effects of nearby
buildings and terrain , and by dynamic effects on more
flexible buildings . Load Cases 2 and 4 in Figure 207 B. 4-8
specifies the torsional loading to 15 percent eccentricity
under 75 percent of the maximum wind shear for Load
Case 2. Although this is more in line with wind tunnel
experience on square and rectangular buildings with
aspect ratios up to about 2.5, it may not cover all cases,
even for symmetric and common building shapes where
larger torsions have been observed. For example , wind
tunnel studies often show an eccentricity of 5 percent or

more under full (not reduced) base shear. The designer
may wish to apply this level of eccentricity at full wind
loading for certain more critical buildings even though it
is not required by the code. The present more moderate
torsional load requirements can in part be justified by the
fact that the design wind forces tend to be upper-bound for
most common building shapes .

In buildings with some structural systems, more severe
loading can occur when the resultant wind load acts
diagonally to the building. To account for this effect and
the fact that many buildings exhibit maximum response in
the across-wind direction (the standard currently has no
analytical procedure for this case), a structure should be
capable of resisting 75 percent of the design wind load
applied simultaneously along each principal axis as
required by Case 3 in Figure 2Q7B.4-S.

For flexible buildings, dynamic effects can increase
torsional loading . Additional torsional loading can occur
because of eccentricity between the elastic shear center
and the center of mass at each level of the structure.
Equation 207B.4-5 accounts for this effect.

It is important to note that significant torsion can occur on
low-rise buildings also (Isyumov and Case 2000) and [
therefore , the wind loading requirements of Section
2 07 B. 4. 6 are now applicable to buildings of all heights .

,4s discussed in Section 207 F, the wind tunnel procedure
should always be considered for buildings with unusual
shapes , rectangular buildings with larger aspect ratios,
and dynamically sensitive buildings . The effects of torsion
can more accurately be determined for these cases and for
the more normal building shapes using the wind tunnel
procedure.

207BA7 Minimum Design Wind Loads

The wind load to be used in the design of the MWFRS for
an enclosed or partially enclosed building shall not be less
than 0.77 kN/m 2 multiplied by the wall area of the building
and 0.38 kN/m 2 multiplied by the roof area of the building
projected onto a vertical plane normal to the assumed wind
direction. Wall and roof loads shall be applied
simultaneously. The design wind force for open buildings
shall be not less than 0.77 kN/m 2 multiplied by the area Af.

Commentaiy:

This section specifies a minimum wind load to be applied
horizontally on the entire vertical projection of the building
as shown in Figure C207B.4-L This load case is to be
applied as a separate load case in addition to the normal
load cases specified in other portions of this chapter .

Association of Structural Engineers of the Philippines, Inc. (ASEP)

2-74 CHAPTER 2 - Minimum Design Loads

Wall Pressure Coefficients, C p

Surface

L/B

Use With

Windward Wall

All values

0.8

0-1

-0.5

Leeward Wall

-0.3

<ih

> 4

-0.2

Side Wall

All values

-0.7

qi,

Roof Pressure Coefficients, for use with q h

Wind

Direction

Windward

Leeward

Angie, 9 (degrees)

Angie, 0 (degrees)

h/L

>60

> 20

Normal

Ridge
for 6 >
10°

<0.25

-0.7

-0.18

-0.5

0.0*

-0.3

0.2

-0.2

0.3

P ©

o P

0.4

0.010

-0.3

-0.5

-0.6

0.5

-0.9

-0.18

-0.7

-0.18

-0.4

0.0*

-0.3

0.2

-0.2

0.2

-0.2

0.3

0.0*

0.4

0.010

-0.5

-0.6

>10

-1.3**

-0.18

-1.0

-0.18

-0.7

-0.18

-0.5

0.0*

-0.3

0.2

-0.2

0.2

0.0*

0.3

0.010

-0.7

-0.6

Normal

Ridge
for 6 <
10 ° and
Parallel
to ridge
for all 9

<0.5

Horizontal distance from
windward edge

*Value is provided for interpolation purposes

**Value can be reduced linearly with area over which
it is applicable as follows

Oto/t/2

-0.9, -0.18

h/2 to h

-0.9, -0.18

h to 2 h

-0.5, -0.18

> 2h

-0.3, -0.1 8

>1.0

0 to h/2

-1.3**, -0.18

Area (m 2 )

Reduction Factor

< 9.3 m 2

1.0

> h/2

-0.7, -0.18

23.2 m 2

0.9

> 92.9 m 2

0.8

Notes:

4 .

6.
1 .

8 .

10. For roof slopes greater than 80°, use C„ = 0.8

Tift

Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

Linear interpolation is permitted for values of L/B , h/L and 9 other than shown. Interpolation shall only be carried out
between values of the same sign. Where no value of the same sign is given, assume 0.0 for interpolation purposes.

Where two values of C p are listed, this indicates that the windward roof slope is subjected to either positive or negative
pressures and the roof structure shall be designed for both conditions. Interpolation for intermediate ratios of h/L in this
case shall only be carried out between C p values of like sign.

For monoslope roofs, entire roof surface is either a windward or leeward surface.

For flexible buildings use appropriate Gy as determined by Section 207B.9.4.

Refer to Figure 207B.4-2 for domes and Figure 207B.4-3 for arched roofs.

Notation:

B = horizontal dimension of building, m, measured normal to wind direction.

L = horizontal dimension of building, m, measured parallel to wind direction.

h = mean roof height in meters, except that eave height shall be used for 6 < 10°
z = height above ground, m

G “ gust effect factor.

q zt Rii = velocity pressure, (N/m 2 ), evaluated at respective height.

9 - Angle of plane of roof from horizontal, °

For mansard roofs, the top horizontal surface and leeward inclined surface shall be treated as leeward surfaces from the
table.

Except for MWFRS at the roof consisting of moment resisting frames, the total horizontal shear shall not be less than that
determined by neglecting wind forces on roof surfaces.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2~75

“•'(Tv

A(h g /D> 1.0)

(K d /D = 0)

(fi D id 2 0.5)

B{hp/D = 0)

B {h g /D £ 0,5)

0 0.1 0.2 0.3 0.4 0.5

Ratio of Rise to Diameter, f/D

External Pressure Coefficients for Domes with a Circular Base
(Adapted from Eurocode, 1995)

Notes;

1. Two load cases shall be considered:

Case A: C p values between A and B and between B and C shall be determined by linear interpolation along arcs on the dome parallel to the wind

direction;

Case B: C v shall be the constant value of A for 0 < 25°, and shall be determined by linear interpolation from 25° to B and from B to C.

2. Values denote C p to be used with q^hD+f) where hD + / is the height at the top of the dome.

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

4. C p is constant on the dome surface for arcs of circles perpendicular to the wind direction; for example, the arc passing through B-B-B and all arcs parallel
to B-B-B.

5. For values of hD/D between those listed on the graph curves, linear interpolation shall be permitted.

6. 0 — 0° on dome spring line, 0 — 90° at dome center top point, f is measured from spring line to top.

7. The total horizontal shear shall not be less than that determined by neglecting wind forces on roof surfaces.

8. For f/D values less than 0.05, use Figure 207B.4-1 .

Figure 207B.4-2

External Pressure Coefficients, C py Domed Roofs Enclosed, Partially Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-76 CHAPTER 2 - Minimum Design Loads

Conditions

Rise-to-span

C P

ratio, r

Windward

Center

Leeward

quarter

half

quarter

Roof on elevated

0 < r < 0.2

-0.9

-0.7-r

-0.5

structure

0.2 < r < 0.3 *

1.5r - 0.3

0
Lq

-0.5

0.3 < r < 0.6

2.75 r - 0.7

-0.7-r

-0.5

Roof springing from
ground level

0 < r < 0.6

1.4r

-0.7-r

-0.5

HVhen the rise-to-span ratio is 0. 2 < r < 0. 3, alternate coefficients given by 6r - 2. 1 shall also be used for
the windward quarter
Notes:

1 . Values listed are for the determination of average loads on main wind force resisting systems.

2. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

3. For wind directed parallel to the axis of the arch, use pressure coefficients from Figure 207B.4-1 with wind directed parallel to ridge.

4. For components and cladding: (i) At roof perimeter, use the external pressure coefficients in Figure 207E.4-2A, B and C with 0 based on spring-line
slope and (2) for remaining roof areas, use external pressure coefficients of this table multiplied by 0.87.

Figure 207B.4-3

External Pressure Coefficients, C p , Arched Roofs, 0.25 < h/L < 1.0
Enclosed, Partially Enclosed Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAP I ER 2 - Minimum Design Loads

■

| 7.5°

■ife

22.5°

j7. 5°

45 °

Wind Direction, y = 0°

Clear Wind Flow I Obstructed Wind

Wind Direction

Clear Wind Flow Obstructed Wind

^nw Cnl

: 2 -

5 Chw ar >d C Nl denote net pressures (contributions from top and bottom surfaces) for windward and leeward half of roof surfaces, respectively.

Clear wind flow denotes relatively unobstructed wind flow with blockage less than or equal to 50%. Obstructed wind flow denotes objects below roof
inhibiting wind flow (> 50% blockage).

f For values of 0 between 7.5° and 45°, linear interpolation is permitted. For values of 0 less than 7.5°, use load coefficients for 0°.

4 Plus and minus signs signify pressures acting towards and away from the top roof surface, respectively.

All load cases shown for each roof angle shall be investigated.

Notation:

L ~ horizontal dimension of roof, measured in the along wind direction, m
h = mean roof height, m

6 Y “ direction of wind, °

0 = angle of plane of roof from horizontal, °

Figure 207B.4-4

Net Pressure Coefficient, C N Monoslope Free Roofs 0 < 45°, y “ 0°, 180°
tj 0.25 < h/L < 1.0 Open Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-78

CHAPTER 2 - Minimum Design Loads

Roof

Angle

Load

Case

Wind Direction, r = 0°, 180°

Clear Wind Flow

Obstructed Wind Flow

C NW

Cnl

C NW

C NL

7. 5°

1.1

-0.3

-1.6

-1

0.2

-1.2

-0.9

-1.7

15°

-0.4

-1.2

-1

0.1

-1.1

-0.6

-1.6

22.5°

1.1

0.1

-1.2

“1.2

-0.1

-0.8

-1.7

30°

1.3

0.3

-0.7

-0.1

-0.9

-0.2

-1.1

37.5°

1.3

0.6

-0.6

-0.2

-0.6

-0.3

-0.9

45°

1.1

0.9

-0.5

-0.3

-0.5

-0.3

-0.7

Notes:

1. C mv and C NL denote net pressures (contributions from top and bottom surfaces) for windward and leeward half of roof surfaces, respectively.

2. Clear wind flow denotes relatively unobstructed wind flow with blockage less than or equal to S0%. Obstructed wind flow denotes objects below root
inhibiting wind flow (> 50% blockage).

3. For values of 9 between 7.5° and 45°, linear interpolation is permitted. For values of 9 less than 7.5°, use monosiope roof load coeffic.ents.

4. Plus and minus signs signify pressures acting towards and away from the top roof surface, respectively.

5. All load cases shown for each roof angle shall be investigated.

6. Notation:

= horizontal dimension of roof, measured in the along wind direction, m

= mean roof height, m

= direction of wind, °

= angle of plane of roof from horizontal , °

Figure 207B.4-5

Net Pressure Coefficient, C N Pitched Free Roofs 6 < 45°, y = 0°, 180°
0.25 < h/L < 1.0 Open Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-79

Roof

Wind Direction, y = 0 °, 180 °

Angle

Load

Clear Wind Flow

Obstructed Wind Flow

Case

Cnw

Cnl

C NW

Cnl

7. 5 °

-i.i

0.3

-1.6

-0.5

-0.2

1.2

-0.9

-0.8

15 °

-1.1

0.4

-1.2

-0.5

0.1

1.1

-0.6

-0.8

22 . 5 °

-1.1

-0.1

-1.2

-0.6

-0.1

0.8

-0.8

30 °

-1.3

-0.3

-1.4

-0.4

-0.1

0.9

-0.2

-0.5

37. 5°

-1.3

-0.6

-1.4

-0.3

0.2

0.6

-0.3

-0.4

45 °

-1.1

-0.9

-1.2

-0.3

0.3

0.5

-0.3

-0.4

:||jv Notes:

§8| l . C NW and C NL denote net pressures (contributions from top and bottom surfaces) lor windward and leeward half of roof surfaces, respectively.

2. Clear wind flow denotes relatively unobstructed wind How with blockage less than or equal to 50 %. Obstructed wind flow denotes objects below root
Jiff : inhibiting wind flow (> 50% blockage).

f8J: 3. For values of 6 between 7.5° and 45°, linear interpolation is permitted. For values of 0 less than 7.5°, use monosiopc roof load coefficients,

jjpj; 4. Plus and minus signs signify pressures acting towards and away from the top roof surface, respectively.

§fe 5. All load cases shown for each roof angle shall be investigated.

Iplg 6. Notation:

L " horizontal dimension of roof, measured in the along wind direction, m

h - mean roof height, m

P§ g, y - direction of wind, °

& - angle of plane of roof from horizontal, °

jjf' Figure 207B.4-6

Net Pressure Coefficient, C N Troughed Free Roofs 8 < 45°, y = 0°, 180°

0.25 < h/L < 1.0 Open Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-80 CHAPTER 2 - Minimum Design Loads

Horizontal

Distance

from

Windward

Edge

Roof Angle

Load Case

Clear Wind
Flow

Obstructed
Wind Flow

C NW

Cni.

< h

All Shapes

-0.8

1.2

e < 45°

0.8

0.5

> h, < 2h

All Shapes

-0.6

-0.9

9 < 45°

0.5

> 2h

All Shapes

-0.3

-0.6

6 <45°

0.3

Notes:

1 . CN denotes net pressures (contributions from top and bottom surfaces).

2. Clear wind flow denotes relatively unobstructed wind flow with blockage less than or equal to 50%. Obstructed wind flow denotes objects below roof
inhibiting wind flow {> 50% blockage).

3. Plus and minus signs signify pressures acting towards and away from the top roof surface, respectively.

4. All load cases shown for each roof angle shall be investigated.

5. For monoslope roofs with theta less than 5 degrees, C N values shown apply also for cases where gamma “ 0 degrees and 0.05 less than or equal to h/ 1
less than or equal to 0.25. See Figure 207B.4-4 for other h/L values.

6. Notation:

L = horizontal dimension of roof, measured in the along wind direction, m

h = mean roof height, m. See Figures 207B.4-4, 207B.4-5 or 207B.4-6 for a graphical depiction of this dimension.

y = direction of wind, °

d = angle of plane of roof from horizontal, °

Figure 207B.4-7

Net Pressure Coefficient, C N Free Roofs 6 < 45°, y = 90°, 270°

0.25 < h/L < 1.0 Open Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-81

t’m

?LX

CASE 1

— T

<»»

— -

&?5P mC

111

J 1 I

Pwr

r lY

^ ZJL ^

H |

£)

M'i

LIT

®.75Piy

0*7$ P pyy

& 7$ P f%Hj£

0,563 P yyy

, 1,

1 4 1 1 1 1 i

—

6.5*3 PffX 5

hhbhw

0.563 P&y

M T — * 0.75 (P iyj^P i$)Bx £% Afj — 0. 75 6? y A/y — 0,505 (P wx^Pij^Px ^ 0*505 ^ ^

ej = £ 0J5 i?r er = ^ 0,/5 By ex = i 0./5 j?v = i 0./5 By

CASE 2

CASE 4

Case 1: Full design wind pressure acting on the projected area perpendicular to each principal axis of the structure, considered
separately along each principal axis.

Case 2: Three quarters of the design wind pressure acting on the projected area perpendicular to each principal axis of the
structure in conjunction with a torsional moment as shown, considered separately for each principal axis.

Case 3: Wind loading as defined in Case 1, but considered to act simultaneously at 75% of the specified value.

Case 4: Wind loading as defined in Case 2, but considered to act simultaneously at 75% of the specified value.

Nolcs:

1. Design wind pressures for windward and leeward faces shall be determined in accordance with the provisions of 207BA1 and 207B.4.2 as applicable
for building of all heights.

2. Diagrams show plan views of building.

3. Notation:

Pwx’Pwy = Windward face design pressure acting in the x, y principal axis, respectively.

Plx^ly ” Leeward face design pressure acting in the x, y principal axis, respectively.
e{e x , e Y ) “ Eccentricity for the x, y principal axis of the structure, respectively.

M r - Torsional moment per unit height acting about a vertical axis of the building.

Figure 207B.4-8

Design Wind Load Cases All Heights

National Structural Code of the Philippines Volume J, 7th Edition, 2015

2-82 CHAPTER 2 - Minimum Design Loads

Part 2: Enclosed Simple Diaphragm Buildings with
h = 48 m

This section has been added to ASCE 7-10 to cover the
common practical cases of enclosed simple diaphragm
buildings up to height h = 48 m. Two classes of buildings
are covered by this method. Class l buildings have h <
18 in with plan aspect ratios L/B between 0.2 and 5.0.
Cases A through F are described in Appendix D, ASCE 7-
10 to allow the designer to establish the lines of resistance
of the MWFRS in each direction so that the torsional load
cases of Figure 207B.4-S need not be considered. Class 2
buildings have 18 m <h< 48 m with plan aspect ratios
of L/B between 0.5 and 2.0. Cases A through E of
Appendix D, ASCE 7-10 are described to allow the
designer to establish the lines of resistance of the MWFRS
so that the torsional load cases of Figure 207 B. 4-8 need
not be considered.

For the type of buildings covered in this method the
internal building pressure cancels out and need not be
considered for the design of the MWFRS. Design net wind
pressures for roofs and walls are tabulated directly in
Tables 207 B. 6-1 and 207 B. 6-2 using the Directional
Procedure as described in Part 1. Guidelines for
determining the exterior pressures on windward, leeward,
and side walls are provided in footnotes to Table 207 B. 6-
L

The requirements in Class 2 buildings for natural building
frequency (7 5 /ft) and structural damping (/? -
1.5% critical) are necessary to ensure that the Gust Effect
Factor, Gp which has been calculated and built into the
design procedure, is consistent with the tabulated
pressures. The frequency of75/h represents a reasonable
lower bound to values found in practice. If calculated
frequencies are found to be lower , then consideration
should be given to stiffening the building. A structural
damping value of 1.5 %, applicable at the ultimate wind
speeds as defined in the new wind speed maps, is
conservative for most common building types and is
consistent with a damping value of 1% for the ultimate
wind speeds divided by 1.6 as contained in the NSCP 2010
(ASCE 7-05) wind speed map. Because Class l buildings
are limited to h < 18 in, the building can be assumed to
be rigid as defined in the glossary , and the Gust Effect
Factor can be assumed to be 0.85. For this class of
buildings frequency and damping need not be considered.

207B.5 General Requirements
207B.5.1 Design Procedure

The procedure specified herein applies to the determination
of MWFRS wind loads of enclosed simple diaphragm
buildings, as defined in Section 207A.2, with a mean roof
height h < 48 m. The steps required for the determination
of MWFRS wind loads on enclosed simple diaphragm
buildings are shown in Table 207B.5-1.

User Note:

Part 2 of Section 207 B is a simplified method for
determining the wind pressures for the MWFRS of
enclosed ' simple diaphragm buildings whose height
h is < 4 m. The wind pressures are obtained directly
from a table. The building may be of any general plan
shape and roof geometry that matches the specified
figures. This method is a simplification of the traditional
“ all heights ” method (Directional Procedure)
contained in Part l of Section 207 B.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-83

Table 207B.5-1

Steps to Determine MWFRS Wind
Loads Enclosed Simple Diaphragm Buildings
( ft <48 m)

Step I :
Step 2:

:: Step 3:

Determine risk category of building or other
structure, see Table 103-1

Determine the basic wind speed, V , for the
applicable risk category, see Figure 207A.5-
1A, BorC

Determine wind load parameters:

> Wind directionality factor, K d , see
Section 207A.6 and Table 207A.6-1

> Exposure category B, C or D, see
Section 207A.7

> Topographic factor, I( zt , see
Section 207A.8 and Figure 207A.8-1

Enclosure classification,
Section 207A.I0

see

Step 4:

Step 5:
Step 6:

Step 7:

Enter table to determine net pressures on
walls at top and base of building respectively,
Vh ,p G , Table 207B.6-1

Enter table to determine net roof pressures.
Table 207B.6-2

Determine topographic factor, K zt , and apply
factor to wall and roof pressures (if
applicable), see Section 207A.8

Apply loads to walls and roofs
simultaneously.

207B.5.2 Conditions

;fn addition to the requirements in Section 207B.1.2, a
building whose design wind loads are determined in
accordance with this section shall meet all of the following
conditions for either a Class 1 or Class 2 building (see
Figure 207B.5-1):

Class 1 Buildings:

F The building shall be an enclosed simple diaphragm
building as defined in Section 207A.2.

2. The building shall have a mean roof height ft < 1 8 m.

The ratio of L/B shall not be less than 0.2 nor more
than 5.0 (0. 2 < L/B < 5. 0).

4. The topographic effect factor K zt =s 1. 0 or the wind
pressures determined from this section shall be
multiplied by K zt at each height z as determined from
Section 207A.8. It shall be permitted to use one value
of K zt for the building calculated at 0.33ft.
Alternatively it shall be permitted to enter the pressure
table with a wind velocity equal to V<jK zt where K zt
is determined at a height of 0. 33ft.

Class 2 Buildings:

1. The building shall be an enclosed simple diaphragm
building as defined in Section 207A.2.

2. The building shall have a mean roof height 18 m
(18 m < ft < 48 m).

3. The ratio of L/B shall not be less than 0.5 nor more
than 2.0 (0.5 < L/B < 2.0).

4. The fundamental natural frequency (Hertz) of the
building shall not be less 75/ft where ft is in meters.

5. The topographic effect factor I( zt = 10 or the wind
pressures determined from this section shall be
multiplied by K zt at each height z as determined from
Section 207 A. 8. It shall be permitted to use one value
of K zt for the building calculated at 0.33 ft.
Alternatively it shall be permitted to enter the pressure
table with a wind velocity equal to V^K zt where K zt
is determined at a height of 0. 33ft.

207B.5.3 Wind Load Parameters Specified in Section
207A

Refer to Section 207A for determination of Basic Wind
Speed V (Section 207A.5) and exposure category
(Section 207A.7) and topographic factor K zt (Section
207A.8).

207B.5.4 Diaphragm Flexibility

The design procedure specified herein applies to buildings
having either rigid or flexible diaphragms. The structural
analysis shall consider the relative stiffness of diaphragms
and the vertical elements of the MWFRS.

Diaphragms constructed of wood panels can be idealized
as flexible. Diaphragms constructed of untopped metal
decks, concrete filled metal decks, and concrete slabs, each
having a span-to-depth ratio of 2 or less, are permitted to
be idealized as rigid for consideration of wind loading.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-84 CHAPTER 2 - Minimum Design Loads

207B.6 Wind Loads— Main Wind Force-Resisting
System

207B.6.1 Wall and Roof Surfaces — Class 1 and 2
Buildings

Net wind pressures for the walls and roof surfaces shall be
determined from Tables 207B.6-1 and 207B.6-2,
respectively, for the applicable exposure category as
determined by Section 207A.7.

For Class 1 building with L/B values less than 0.5, use
wind pressures tabulated for L/B — 0.5. For Class 1
building with L/B values greater than 2.0, use wind
pressures tabulated for L/B = 2.0.

Net wall pressures shall be applied to the projected area of
the building walls in the direction of the wind, and exterior
side wall pressures shall be applied to the projected area of
the building walls normal to the direction of the wind
acting outward according to Note 3 of Table 207B.6-1,
simultaneously with the roof pressures from Table 207B.6-
2 as shown in Figure 207B.6-I .

Where two load cases are shown in the table of roof
pressures, the effects of each load case shall be investigated
separately. The MWFRS in each direction shall be
designed for the wind load cases as defined in Figure
207B.4-S.

Exception:

The torsional load cases in Figure 20? B 4-8 (Case 2 and
Case 4) need not he considered for buildings which meet
the requirements of Appendix 0. ASCE 7-10,

Commentary:

Wall and roof net pressures are shown in Tables 207 8. 6-1
and 2078,6-2 and are calculated using the external
pressure coefficients in Figure 207 B, 4-1. Along wind net
wall pressures are applied to the projected area of the
building walls in the direction of the wind, and exterior
sidewall pressures are applied to the projected area of the
building walls normal to the direction of the wind acting
outward [ simultaneously with the roof pressures from
Table 2078,6-2 . Distribution of the net wall pressures
between windward and leeward wall surfaces is defined in
Note 4 of Table 2078,6-1. The magnitude of exterior
sidewall pressure is determined from Note 2 of Table
207B. 6-1. It is to be noted that all tabulated pressures are
defined without consideration of internal pressures
because internal pressures cancel out when considering
the net effect on the MWFRS of simple diaphragm
buildings . Where the net wind pressure on any individual

wall surface is required, internal pressure must he , |§f
included as defined in Part 1 of Section 207 B.

The distribution of wall pressures between windward and ffj
leeward wall surfaces is useful for the design of floor and |
roof diaphragm elements like drag strut collector beams, JJJ
as well as for MWFRS wall elements. The values defined in |f
Note 4 of Table 2078.6-1 are obtained as follows: The J§f
external pressure coefficient for all windward walls is ;§§
C p = 0.8 for all L/B values . The leeward wall C p value is Jj
(-0.5) for L/B values from 0.5 to 1.0 and is (-0.3) for L/B
= 2. 0. Noting that the leeward wall pressure is constant for W
the full height of the building, the leeward wall pressure jj|
can be calculated as a percentage of the Pi t value in the. Jjj
table. The percentage is 0. 5/(0. 8 + 0.5) x 100 - 38% for :j§f
L/B = 0.5 to 1.0. The percentage is 0.37(0.8+0.3) x 1 00 =» jj
27% for L/B = 2.0 . Interpolation between these two fp
percentages can be used for L/B ratios between 1.0 ami |j
2.0. The windward wall pressure is then calculated as the ; Iff
difference between the total net pressure from the table \ §J,
using the p h and p 0 values and the constant leeward wall |j
pressure.

Sidewall pressures can be calculated in a similar manned ||j
to the windward and leeward wall pressures by taking a >
percentage of the net wall pressures. The C p value fan j§|
sidewalls is (-0.7). Thus , for L/B = 0.5 to 1.0, the |j
percentage is 0. 7/(0. S + 0.5) x 100 - 54%. For L/B = 2, Or :|J|L
the percentage is 0. 7/(0. 8 + 0.3) * 100 ~ 64%. Note that ||i
the sidewall pressures are constant up the full height of the |j
building.

The pressures tabulated for this method are based on jjj.
simplifying conservative assumptions made to the different jjj
pressure coefficient ( GC p ) cases tabulated in Figure |j|
207 B. 4- 1, which is the basis for the traditional all heights Jjti
building procedure (defined as the Directional Procedure |||
in this code) that has been a part of the standard since ;jj|
1972. The external pressure coefficients C p for roofs have ^
been multiplied by 0.85 , a reasonable gust effect factor for ^
most common roof framing, and then combined with an ij
internal pressure coefficient for enclosed buildings (plus or jjg
minus 0. 18) to obtain a net pressure coefficient to serve as Jjj
the basis for pressure calculation. The linear wall pressure |g
diagram has been conceived so that the applied pressures. Iff
from the table produce the same overturning moment as the Jj|
more exact pressures from Part 1 of Section 207 B. For jjj
determination of the wall pressures tabulated, the actual gjj
gust effect factor has been calculated from Equation
207 A. 9-10 based on building height, wind speed , exposure , jjf
frequency , and the assumed damping value.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-85

207B.6.2 Parapets

The effect of horizontal wind loads applied to all vertical
surfaces of roof parapets for the design of the MWFRS
shall be based on the application of an additional net
horizontal wind pressure applied to the projected area of
the parapet surface equal to 2.25 times the wall pressures
tabulated in Table 207B.6-1 for L/B = 1.0. The net
pressure specified accounts for both the windward and
leeward parapet loading on both the windward and leeward
building surface. The parapet pressure shall be applied
simultaneously with the specified wall and roof pressures
shown in the table as shown in Figure 207B.6-2. The height
h used to enter Table 207 B. 6-1 to determine the parapet
pressure shall be the height to the top of the parapet as
shown in Figure 207B.6-2 (use h — lip).

Commentary:

ttr

The effect of parapet loading on the MWFRS is specified in
Section 207 BA. 5 of Part 1. The net pressure coefficient for
the windward parapet is +1.5 and for the leeward parapet
is ~~ l .0. The combined effect of both produces a net
coefficient of +2.5 applied to the windward surface to
Account for the cumulative effect on the MWFRS in a
Simple diaphragm building . This pressure coefficient
compares to a net pressure coefficient of 1.3 Gf for the
tabulated horizontal wall pressure p fl at the top of the
building. Assuming a lower-bound gust factor
Gf = 0. 85, the ratio of the parapet pressure to the wall
pressure is 2.57(0.85 *1.3) - 2.25. Thus . a value of 2.25 is
assumed as a reasonable constant to apply to the tabulated
wall pressure p h to account for the additional parapet
loading on the MWFRS.

207B.6.3 Roof Overhangs

The effect of vertical wind loads on any roof overhangs
| shall be based on the application of a positive wind
pressure on the underside of the windward overhang equal
to 75% of the roof edge pressure from Table 207B.6-2 for
Zone 1 or Zone 3 as applicable. This pressure shall be
applied to the windward roof overhang only and shall be
applied simultaneously with other tabulated wall and roof
pressures as shown in Figure 207B.6-3.

Commentary:

The effect of vertical wind loading on a windward roof
overhang is specified in Section 207 BA. 4 of Part 1. A
positive pressure coefficient of +0.8 is specified. This
compares to a net pressure coefficient tabulated for the
windward edge zone 3 of —1.06 (derived from
0.85 x -1.3 x 0.8 - 0.18). The 0.85 factor represents the
gust factor G, the 0.8 multiplier accounts for the effective
wind area reduction to the 1.3 value of C p specified in
Figure 207 BA-1 of Part 1, and the - 0.18 is the internal
pressure contribution. The ratio of coefficients is 0.8/1.06
- 0.755. Thus , a multiplier of 0.75 on the tabulated
pressure for zone 3 in Table 207 B. 6-2 is specified.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-86

CHAPTER 2 - Minimum Design Loads

0.21 < B < 5L

CLASS 1 BUILDING

O 5L < B < 2 L

PLAN

CLASS 2 BUILDING

ELEVATION

Note: Roof form may be flat, gable, mansard or hip

Figure 207B.5-1

Building Geometry Requirements Building Class, h < 48 m
Enclosed Simple Diaphragm Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-87

SEE FIGURE 207B.6-2 FOR

PARAPET WIND PRESSURES ROOF PRESSURES

ELEVATION

Figure 207 B. 6-1

Application of Wind Pressures Wind Pressures - Walls and Roof, ft < 48 m
Enclosed Simple Diaphragm Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-88 CHAPTER 2 - Minimum Design Loads

Figure 20 7 B. 6-2

Application of Parapet Wind Loads Parapet Wind Loads, h < 48 m
Enclosed Simple Diaphragm Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-89

Enclosed Simple Diaphragm Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

PLAN

WIND PRESSURE ELEVATION

Notes to Wall Pressure Table 207B.6-1 :

1 . From table for each Exposure (B C or D), V, L/B and h, determine p h (top number) and p„ (bottom number) horizontal along-wind net wall pressures
“ L 't < a {' o“‘P re ” f b ( e . umform over ‘ hc 'I a " surfa / cc acti "S ou t wa rd and shall be taken as 54% of the tabulated p h pressure for 0. 2 <

n^c! y al °" S 7 ind " et . W f P^^resas shown above to the projected area of the building walls in the direction of the wind and apply external side wall

Distribution of tabuhmf °ii ^ Wal ' S n ° rm , al ‘° dlrection wind ’ simultaneously with the roof pressures from Table 207B.6-2.

Distribution of tabu ated net wall pressures between windward and leeward wall faces shall be based on the linear distribution of total net pressure with

38% ofm'forO T kT/B oSndVvv T T"?' fm™? assumed uniformly distributed over the leeward wall surface acting outward at
^ \ 11 u ~v l “I 1 ^ J1 ^ ^ /0 °^ /l or ^ ® — 5*0’ Linear interpolation shad be used for 1 0 < L/B <20 The remaininf? net

^ pre “" re “ ine - ” r “- «— - “'•» r~ »

Interpolation between values of V, h and L/B is permitted.

Notation:

L “ building plan dimension parallel to wind direction, m

B = building plan dimension perpendicular to wind direction, m

h - mean roof height, m

Vh>Po ~ along-wind net wall pressure at top and base of building respectively. Pa

Figure 207B.6-1

Application of Wall Pressures Wind Pressures - Walls, h < 48 in
Enclosed Simple Diaphragm Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads ,

Table 207B.6-1

MWFRS - Part 2: Wind Loads - Walls (kN/nr)
Exposure B

V ( kph )

150

200

250

iUU

h ( m ),
r /r

0.5

2 0.5

1 2

0.5

1 2

1.24

1.22

1.09

2.39

2.36

2.15

4.03

3.96

3.63 6.25

6.11 5.61

9.14

8.90 8.17

0.83

0.82

0.67

1.61

1.59

1.33

2.72

2.67

2.24 4.22

4.12 3.47

6.17

6.00 5.09

1.20

1.19

1.06

2.31

2.29

2.08

3.88

3.82

3.50 6.00

5.88 5.40

8.76

8.57 7.86

0.82

0.81

0.66

1.58

1.56

1.30

2.65

2.61

2.19 4.09

4.01 3.39

5.96

5.81 4.96

1.16

1.15

1.03

2.23

2.21

2.00

3.73

3.68

3.37 5.75

5.64 5.19

8.38

8.17 7.51

0.79

0.80

0.65

1.54

1.53

1.27

2.57

2.54

2.14 3.97

3.89 3.30

5.83

5.64 4.79

1.13

1.12

1.00

2.14

2.13

1.93

3.57

3.53

3.23 5.49

5.40 4.97

7.97

7.82 7.22

0.78

0.79

0.64

1.50

1.49

1.25

2.50

2.47

2.09 3.84

3.78 3.21

5.58

5.47 4.66

1.08

1 09

0.96

2.06

2.05

1.85

3.42

3.38

3.09 5.23

5.15 4.74

7.56

7.43 6.86

0.77

0.64

1.46

1.45

1.22

2.42

2.40

2.03 3.71

3.66 3.12

5.39

5.27 4.54 ]

1.04

1.05

0.93

1.98

1.97

1.77

3.26

3.23

2.94 4.97

4.90 4.51

7.20

7.05 6.55

0.76

0.63

1.43

1.42

1.19

2.35

2.33

1.98 3.58

3.54 3.03

5.18

5.10 4.37

1.01

1.00

0.89

1.90

1.88

1.69

3.10

3.08

2.80 4.70

4.65 4.27

6.79

6.64 6.15

0.73

0.74

0.61

1.39

1.38

1.16

2.27

2.26

1.92 3.45

3.41 2.93

5.01

4.86 4.23

0.97

0.96

0.86

1.85

1.80

1.60

2.94

2.92

2.65 4.43

4.39 4.02 1

6.51

6.28 5.72

0.73

0.72

0.60

1.35

1.34

1.13

2.20

2.19

1.86 3.32

3.28 2.83

4.75

4.62 4.08

0.93

0.92

0.81

1.71

1.52

2.77

2.76

2.49 4.16

4.13 3.77

5.93

5.88 5.41

0.71

0.72

0.60

1.31

1.10

2.12

2.11

1.80 3.18

3.16 2.72

4.53

4.50 3.88

0.88

0.89

0.77

1.62

1.61

1.43

2.60

2.59

2.33 3.88

3.86 3.50

5.52

5.45 4.97

0.69

0.57

1.27

1.07

2.04

1.74 3.05

3.03 2.61

4.35

4.27 3.71

0.83

0.85

0.73

1.52

1.34

2.43

2.42

2.16 3.60

3.58 3.23

5.07

5.03 4.59

0.68

0.55

1.23

1.03

1.97

1.96

1.67 2.91

2.90 2.50

4.06

4.08 3.55

0.78

0.69

1.41

1.24

2.25

1.99 3.31

3.30 2.95

4.60

4.56 4.13

0.65

0.56

1.19

1.00

1.89

1.61 2.78

2.77 2.39

3.89

3.85 3.34

0.74

0.63

1.31

1.14

’ 2.07

2.07

1.82 3.03

3.03 2.69

4.20

4.20 3.77

0.65

0.63

0.52

1.15

0.97

1.82

1.55 2.66

2.66 2.29

3.67

3.69 3.22

0.67

0.57

1.19

1.03

1.88

1 .64 2.74

2.74 2.40

’ 3.77

3.77 3.31

0.62

0.53

1.10

0.94

1.74

1.49 2.53

2.53 2.19

3.46

3.46 3.05

0.59

0.51

1.07

0.93

1.68

1.46 2.43

2.43 2.12

3.33

3.33 2.93

0.59

0.51

1.05

0.91

1.65

1.43 2.39

2.39 2.08

3.27

3.27 2.8'

0.38

” 0.38

0.33

0.67

0.58

1.05

0.91 1.51

1.51 1.33

2.04

2.04 1.85

0.38

0.33

0.67

0.58

. 1.05

1.05

0.91 1.51

1.51 1.33

; 2.04

2.04 1.81

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-92 CHAPTER 2 - Minimum Design Loads

Table 207B.6-1

MWFRS - Part 2: Wind Loads - Walls (IcN/m 2 )
Exposure C

V (kph)
h (m),
L/B

1.58 1.42

1.16 0.97

1.55 1.38

1.16 0.96

1.51 1.33

1.13 0.94

0.5

3.10

3.06

2.75

5.21

5.11

4.62

8.04

2.28

2.25

1.89

3.83

3.76

3.19

5.92

3.01

2.97

2.68

5.06

5.04

4.49

7.79

2.24

2.21

1.87

3.75

3.74

3.13

5.78

2.92

2.89

2.60

4.90

4.87

4.36

7.53

2.19

2.17

1.85

3.67

3.65

3.07

5.65

7.85 7.10

5.77 4.89

7.61 6.89

5.65 4,81

7.37 6.68

5.53 4.71

1.01

.00 1 0.83

1.96 1.95

2.34 2.08 3.83 3.81 3.42 5.78

1.92 1.91 1.63 3.12

2.24 2.24 1.98 3.63

2 2.99 2.59 4.53

3 3.42 3.05

2.92 I 2.75 I 2.51

4.82

4.18

6.94

6.88

4.18

5.72

5.19

8.28

8.11

5.19

4.66

4.05

6.72

6.61

4.05

1.86

2.13 I 2.13 1.88

2.07 1.81

2.01 2.01

3.21 2.85

2.81

4.17

3.01 I 2.99 I 2.63 I 4.41

3.05 3.77

4.75 4.25

4.16 I 3.63_
4.39 I 3.90

6.58

5.60

3.92

7.26

7.16

4.58

7.21

1.94

3.77

0.56 0.56

0.56 0.56 0.49

.60 1.60 1.38

.58 1.58 1.36

.0! 1.01 0.88 1.59

2.71 1 2.71 I 2.34
.51 I 2.87 2.76 2.41

.38 2.55

.36 2.49

3.98 I 3.47
4.02 1 3.53

2.25

3.80

2.40

3.65

2.37

3.60

1.38

2.30

3.79 3.30

3.18

1.0) I 1.01 I 0.88 I 1.59 1.59 1.38 2.30

QgSEDEIEBHEESIB^I

2.30 2.00 3.14
2.30 2.00 3.14

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2

Table 207B.6-1

MWFRS - Part 2: Wind Loads - Walls (kN/m 2 )
Exposure D

3.50 3.45 3.08 5.87 5.75 5.15 9.00

2.70 2.66 2.25 4.52 4.43 3.76 6.93

3.42 3.37 3.01 5.72 5.61 5.02 8.76

2.66 2.62 2.22 4.44 4.36 3.70 6.80

3.33 3.29 2.94 5.56 5.46 4.89 8.51

2.61 2.58 2.19 4.36 4.28 3.65 6.66

5.40 5.31 4.76 I 8.24

3.24 I 3.21

2.54 2.16 I 4.27

3.12 2.78

\msm

I 2.52 I 2.49

1.87 1.61

1.57

1.28 I

1.52

1.25 1.26

1.48 1.47

.25 1.24

i 06 1 3.03 1 2.70 | 5.05
2.47 2.45 2.08 4.08 1 4,03

2.62 4.87 4.82

59 I 6.52
62 7.97

3.52 I 6.37

7.69

8.79 7.86

6.77 5.74

8.56 7.67

6.65 5.65

8.33 7.46

6.52 5.56

6.39 5.46

7.82 7.03

6.25 5.36

7.55 I 6.80

2.41 I 2.40 I 2.05

2.52 4.68

2.35 I 2.01 3.88

2.75 I 2.74 2.43 4,49

2.31 2.30 1.97 3.78 I 3.75 | 3.24

64 2.63 2.32 4.28 I 4.26

4.16 7.08

5.95 I 5.14

6.99 6.29

K&illB&ui

QUEUES ^^9 El£3

5.79

5.02

8.35 !

8.26

1.39

1.19

1.32

1.19 1.17

1.26 1.24

1.16 1.14

1.19 1.17

1.13

0.96

1.09

0.93

1.09

0.93

0.70

0.60

0.70

0.60

26 I 2.25 1.93 3.67 3.65

2.52 I 2.52 I 2.22 4.07 4.05 1 3.60 1 6.07

2.21 I 2.20 | 1.88 3.56 3.54 3.06 5.31

2.40 2.10 3.85 3.83 3.39 5.70

2.14 1.84 3.44 3.43 2.97 5.10

I 2.27 I 2.27 1.97 3.61 3.61 3.16 5.3

I 2.09 I 2.09 I 1.79 I 3.36 3.32

I 2.12 I 2.12 1.83

1.73

1.97

1.95 1.95

6.68 6.01

5.62 4.89

I 6.36 I 5.72

1 5 - 45 1 zJl

61)3 I 5.40
5.27 1 4.60

9.51

8.60

7.94

6.95

5.67

5.06

7.99

7.98

7.16

5.08 4.43

5.30

4.69

7.40

7.38

3.20 2.76 I 4,68

3.09 I 3.09 2.68 4.49

3.06 3.06 2.65 I 4.45

1.25 | 1.25 | 1.08 1 1.96 1.96 1.70 2.83

1.25 1.25 1.08 1.96 1.96 1.70 2.83

4.88 4.26

1 490 4,30

I 4.67 4.07

4.49 3.91

3.86

2.83 2.47

National Structural Code of the Philippines Volume I, 7th Edition, 2015

Notes to Roof Pressure Table 207B.6-2:

1. From table for Exposure C, V , h and roof slope, determine roof pressure for each roof zone shown in the figures for the applicable roof form. For
other exposures B or D, multiply pressures from table by appropriate exposure adjustment factor as determined from figure below.

2. Where two load cases are shown, both load cases shall be investigated. Load case 2 is required to investigate maximum overturning on the building from
roof pressures shown.

3. Apply along-wind net wall pressures to the projected area of the building walls in the direction of the wind and apply exterior side wall pressures to the
projected area of the building walls normal to the direction of the wind acting outward, simultaneously with the roof pressures from Table 207B.6-2.

4. Where a value of zero is shown in the tables for the fiat roof case, it is provided for the purpose of interpolation.

5. Interpolation between V> h and roof slope is permitted.

Figure 207B.6-2

Application of Roof Pressures Wind Pressures - Roofs, h < 48 m
Enclosed Simple Diaphragm Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

\ ©

~v©--

Flat Roof
(8 < 10 def$

&*>

Gable Roof

Hip Roof

\\0i

Monoslope

Roof

Mansard Roof

Figure 207B.6-2

Application of Roof Pressures Wind Pressures - Roofs, h < 48 m
Enclosed Simple Diaphragm Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

CHAP i ER 2 - Minimum Design Loads

2-97

Table 207B.6-2

MWFRS - Part 2: Wind Loads - Roof (kN/m 2 )
MWFRS - Roof, V = 300 - 350 kph, h =* 3 - 12 m
Exposure C

K (kph)

300

350

Zone

Flat <2:12 {9.46°)

-3.99

-3.56

-2.92

-2.38

-2.12

-1.74

■HIM

0.00

BAM

0.00

3:12 { 14.0°)

BSA?»B

M««

m>x%w

Bill

B3I1M

BWilB

BAM

IBfilrM

■♦him

mxzm

BAM

■♦HIM

■(HIM

4: 12(18.4°)

-3.22

-2.60

-3.99

-3.56

-2.92

-1.91

■Bl

mmm

WfM¥M

mwLU

m*¥m

■WIM

mmm

BAM

BA<tm

■♦HIM

Bihim

Mum

5:12(22.6°)

w>wm

BMi

BTCSB

BAM

EBB

mktm

mwm

Bl^|

Bwim

mmm

BfilW

BAM

BAM'

6:12(26.6°)

BAM

MEM

M ?>■

MSB

Bir/B

■w

BAfli'B

ikmiM

mmm

■♦HIM

9:12(36.9°)

BlfeM

wkKZM

B9ESB

mmm

BUM

■♦HIM

MiM

BAM

BikM

B»hhB

mmm

12:12(45.0°)

HAM

MUM

B»T«

ihpb

ESEfl

WKWM

mwrm

faiitM

BAM

mimm

■IHIM

BiKEB

BAM

BAMI

Flat <2:12 (9.46°)

BScMtEB

warnm

BiftB

mxnm

■aw

■♦him

BAM

MSESM

■♦HIM

■♦him;

3:12(14.0°)

■MEHB

BKl

tatea

wswm

mmm

0.53

-0.75

0.00

mmm

0.00

BAM

-0.47

BAiTiB

4: 12(18.4°)

IMBIM

EEEI

Mra

mm&m

wrxLm

bum

BEAM

mwm

ESDI

BUM

mmm

BAiliB

Miim

mmm

■hmm

■♦HIM

BAM

■♦HIM

5:12(22.6°)

WEIl

ME EB

IfclrM

mwm

BB1

-2.34

-2.09

-1.71

1.40

-1.17

0.00

BAM

MAM

0.68

-0.73

0.00

6:12(26.6°)

mwsM

EBB

■MM

BcltEB

ISMil

fapM

BEAM

toPrJg

BUM

Bllrl

bam

BAM

HiMM

BAM

9:12(36.9°)

■m

Bill

EBB

mtm&m

BArJB

BfftM

Btjli

BEAM

HfByp

BBiB

BAM

■(HIM

Bill

BEES

BAM

12:12(45.0°)

El£fl

BIE1

BflEfiB

BBl

BAM

mxrm

1.84

-1.17

0.00

BAM

1.15

-0.73

0.00

Flat <2:12 (9.46°)

B^B

BBW

mimm

b*im

BAM

WTM

HSEB

mmm

BTC7AB

B'?M

BAM

3:12(14.0°)

wswm

MiM

■ffia

Bi*l

BAM

BEAM

MEM

mem

Milili

BAM

■(*»■

■♦**■

■(HIM

■♦him

■♦HIM

4: 12(18.4°)

BJW;B

wrxvm

BSTM

MfrKB

■w mm

B^l

BAM

BSi I

BAM

BiFM

BAM

Bihim

5:12(22.6°)

-2.23

-2.25

-3.45

-3.08

-2.52

-1.49

-1.50

-2.31

-1.69 1

■H

1,28

HiVB

0.00

0.24

-0.72

0.00

BAM

WEESM

6:12(26.6°)

-1.79

-2,25

-3.45

-3.08

-2.52

-1.20

-1.50

-2.31

-2.06

-1.69

1.42

-1.07

BAM

■SB

0.00

0.95

-0.72

0.00

-1.04

-2.25

-3.45

-3.08

-2.52

fcllfUl

-1.50

-2.31

-2.06

-1.69

1.69

-1.07

0.00

BAM

1.13

Bi1r>B

0.00

-0.58

-2.20

-3.45

-3.08

-2.52

-0.39

BIEfiB

-2.31

-2.06

-1.69

1.69

-1.07

0.00

1.09

BAM

BEES

BAMI

Flat <2:12 (9.46°)

-3.05

-2.72

-2.23

-2.27

-2.03

-1.66

0.00

Ilil

0.00

3:12(14.0°)

ESS 1

MFftB

BAM

1CTM

mrxxm

BKM

wrxxm

Biiiti

EBB

0.43

-0.61

0.00

mmm

BAMI

-0.07

0.00

4: 12(18.4°)

-2.46

-1.98

-3.05

-2.72

-2.23

-1.83

-1.48

-2.27

-2.03

-1.66

0.85

-0.S7

0.00

0.64

-0.65

BAM

0.00

5:12(22.6°)

EKSKB

WEEM

BIB

Bllrl

mmm

BAM

BEAM

warn

BflffB

mmm

BAM

BArJB

BAM

iai

6:12(26.6°)

■KM

■JEM

WMTW

MEM

BOOB

Bg[:l

BAM

mwm

■(HIM

■♦HIM

MMM

B3EB

BflHB

BAtTiB

BAM

9:12(36.9°)

-0.92

-1.98

-3.05

-2.72

-2.23

-0.68

-MS

-2.27

-2.03

-m

■EIS

ES2B

■lUlTli

■♦HIM

BIPB

WS5M

BE9

BAM

12:12(45.0°)

-0.52

-0.44

-3.05

-2.72

-2.23

m\*vm

EES

mwm

mmtu

EBB

1,49

-0.95

BAM

0.00

19.8

-12.5

0.0

0.0 !

National Structural Code of the Philippines Volume L 7th Edition, 2015

2-100 CHAPTER 2 - Minimum Design Loads

Table 207B.6-2

M WFRS - Part 2; Wind Loads - Roof (kN/m 2 )
MWFRS - Roof, V “ 150 -250 kph, h = 27- 36 m
Exposure C

3:12 (14.0°)

4: 12(18.4°)

5:12(22.6°)

6:12(26.6°)

6:12(36.9°)

12:12(45.0°)

Flat <2:12 (0.46°)
3:12(14.0°)

4: 12(18.4°)
5:12(22.6°)
6:12(26.6°)
9:12(36.9°)

12:12(45.0°)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

Table 207B.6-2

MWFRS - Part 2: Wind Loads - Roof (kN/m 2 )
MWFRS - Roof, V = 300 - 350 kph, ft = 27 - 36 m
Exposure C

K (kph)

Roof Slope

Rat <2:12 (9.46°)
3:12(14.0°)

4: 12(18.4°)

5:12(22.6°)

6:12(26.6°)

4: 12(18.4°)

5 : 12 ( 22 . 6 °)

6:12(26.6°)

SNV '

$C '

Flat <2:12 (9.46°)

3:12(14.0°)

H§

4: 12(18.4°)

Wl '

£{fj, %

5:12(22.6°)

$$$& v|y : *f

6:12(26.6°)

9:12(36.9°)

12:12(45.0°)

Flat <2:12 (9.46°)

3:12(14.0°)

4: 12(18.4°)

5 : 12 ( 22 . 6 °)

6:12(26.6°)

9:12(36.9°)

12:12(45.0°)

l»l^B!rCT»^tMMi»iMgTiinigiT^MgiT«»iTr«»iTiTMgTi , ail

I ggMgaCTMfMggUfcMMM IriB B nCTgtjc^ MrMlgEMl

|g>lrMgf>MMtxilt^||»!lfM|

IMiBCMMEWIf ■WiltMjMHnyiUMGMMEMMBMl

lEjBaroiBBiBBiroiillBiBaigil

National Structural Code of the Philippines Volume I, 7th Edition, 2015

CHAPTER 2 - Minimum Design Loads

Table 207B.6-2

MWFRS - Part 2: Wind Loads - Roof (kN/m 2 )
MWFRS - Roof, V = 150- 250 kph, h = 39 - 48 m
Exposure C

5:12(22.6°)

6:12(26.6°)

BMlBI— iliMIil MMBP W — M— TOM

9:12(36.9°)

12:12(45.0°)

TJai <2:12 (9.46°)

3:12(14.0°)

4: 12(18.4°)

5:12(22.6°)

6:12(26.6°)

9:12(36.9°)

12:12(45.0°)

Flat <2:12 (9,46°)

3:12(14.0°)

4: 12(18.4°)
5:12(22.6°)
6:12(26.6°)
9:12(36.9°)

0.00 0.00

12:! 2 (45.0°)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

Table 207B.6-2

MWFRS - Part 2: Wind Loads - Roof (kN/m 2 )
MWFRS - Roof, V “ 300 - 350 kph, h = 39 - 48 m
Exposure C

WMM

mmrn

EIiM

MTtTia

ilia

giliM

WEM

4 : 12 ( 18 . 4 °)

Bia

mbkiM

mnm

Bifii

E XLM

EMI

MtWfrM

ETiM

MEM

mwnm

Hj'iTiTtlh

m%zm

IBM

EltM

5 : 12 ( 22 . 6 °)

WSEM

BKltl

WAM¥m

«EE»

WSSM

MWtM

1.90

- 1.59

0.00

0.85

- 0.71

0.00

EMI

6 : 12 ( 26 . 6 °)

- 2.66

- 3.33

- 5.12

- 4.56

- 3.74

- 1.18

- 1.48

- 2.27

EMI

ElftfM

2,10

- 1.59

0.00

0.93

- 0.71

0.00

warn

9 : 12 ( 36 . 9 °)

- 1.54

- 3.33

- 5.12

- 4.56

- 3.74

- 0.68

- 1.48

- 2.27

mvm

EIMM

2.51

- 1.59

0.00

1.12

- 0,71

0.00

ekm

12 : 12 ( 45 . 0 °)

- 0.87

- 3.33

- 5.12

- 4.56

- 3.74

- 0.39

- 1.48

- 2.27

mwvm

mwxm

2.51

- 1.59

0.00

0,00

0.00

19.8

- 12.5

0.0

tow

HEE

National Structural Code of the Philippines Volume I, 7th Edition, 2015

CHAPTER 2 - Minimum Design Loads 2-105

207C.3 Velocity Pressure Table 207C.2-1

Steps to Determine Wind Loads on MWFRS

207C.3.1 Velocity Pressure Exposure Coefficient Low-Rise Buildings

Based on the Exposure Category determined in Section
207A.7.3, a velocity pressure exposure coefficient K z or
Kb? as applicable, shall be determined from
Table 207C.3-1.

For a site located in a transition zone between exposure
categories that is near to a change in ground surface
roughness, intermediate values of K z or K h , between those
shown in Table 207C.3-1, are permitted, provided that they
are determined by a rational analysis method defined in the
recognized literature.

Step 1:

Determine occupancy category of building or
other structure, see Table 103-1

Step 2:

Determine the basic wind speed, V, for the
applicable risk category, see Figure 207A.5-
1A, B or C

Step 3:

Determine wind load parameters:

> Wind directionality factor, K d , see
Section 207A.6 and Table 207A.6-1

> Exposure category B, C or D, see
Section 207A.7

> Topographic factor, K zt , see Section
207A.8 and Figure 207A.8-1

> Enclosure classification, see

Section 207A.10

> Internal pressure coefficient, (GC p i), see
Section 207A.1 1 and Table 207A.1 1-1

Step 4:

Determine velocity pressure exposure
coefficient, K z or K h , see Tables 207C.3-1

Step 5:

Determine velocity pressure, q z or q h , see
Equation 207C.3-1

Step 6:

Determine external pressure coefficient,
(CG p ), using Figure 207C.4-1 for flat and
gable roofs.

User Note:

See Commentary Figure C207C.4-1 for guidance On hip
roofs .

Step 7: Calculate wind pressure, p, from
Equation 207C.4-1

National Structural Code of the Philipp 1,

Volume I, 7th Edition, 2015

2-106

CHAPTER 2 Minimum Design Loads

Commentary:

See commentary to Section C207B.3.1.

207C.3.2 Velocity Pressure

Velocity pressure, q z , evaluated at height z shall be
calculated by the following equation:

q z = 0. 613 K z K zt K d V 2 (N/m 2 ); V in m/s (207C.3-1)

where

K d =

wind directionality factor, see Section
207A.6

Kz =

velocity pressure exposure coefficient, see
Section 207C.3.1

Kzt =

topographic factor defined, see Section
207A.8.2

basic wind speed, see Section 207A.5.1

Qz =

velocity pressure calculated using

Equation 207C.3-1 at mean roof height h

The numerical coefficient 0.613 shall be used except where
sufficient climatic data are available to justify the selection
of a different value of this factor for a design application.

Commentary:

See commentary to Section C207B.3.2 .

Loads on Main Wind-Force Resisting Systems:

The pressure coefficients for MWFRS are basically
separated into two categories:

1. Directional Procedure for buildings of all heights
(Figure 207B.4-1) as specified in Section 207B for
buildings meeting the requirements specified therein.

2. Envelope Procedure for low-rise buildings
(Figure 207C.4-1) as specified in Section 207 C for
buildings meeting the requirements specified therein.

In generating these coefficients, two distinctly different
approaches were used. For the pressure coefficients given
in Figure 207 B. 4-1, the more traditional approach was
followed and the pressure coefficients reflect the actual
loading on each surface of the building as a function of
wind direction, namely, winds perpendicular or parallel to
the ridge line.

For low-rise buildings, however, the values of (GC v f)
represent “pseudo ” loading conditions that, when applied
to the building, envelop the desired structural actions

(bending moment, shear, thrust) independent of wind
direction. To capture all appropriate structural actions
the building must be designed for all wind directions by
considering in turn each corner of the building as the
windward or reference corner shown in the eight sketches
of Figure 207C.4-1. At each corner, two load patterns are
applied, one for each wind direction range. The end zone
creates the required structural actions in the end frame or
bracing. Note also that for all roof slopes, all eight load
cases must be considered individually to determine the
critical loading for a given structural assemblage or
component thereof. Special attention should be given to
roof members, such as trusses, which meet the definition of
MWFRS but are not part of the lateral resisting system .
When such members span at least from the eave to the ridge
or support members spanning at least from eave to ridge,
they are not required to be designed for the higher end zone
loads under MWFRS. The interior zone loads should be
applied. This is due to the enveloped nature of the loads for
roof members.

To develop the appropriate “pseudo” values of (GC p f),
investigators at the University of Western Ontario
(Davenport et al 1978) used an approach that consisted
essentially of permitting the building model to rotate in the
wind tunnel through a full 360° while simultaneously
monitoring the loading conditions on each of the surfaces
(Figure C207C.4-1). Both Exposures B and C were
considered. Using influence coefficients for rigid frames, it
was possible to spatially average and time average the
surface pressures to ascertain the maximum induced
external force components to be resisted . More
specifically, the following structural actions were
evaluated:

1. Total uplift.

2. Total horizontal shear.

3. Bending moment at knees (two-hinged frame).

4. Bending moment at knees (three-hinged frame).

5. Bending moment at ridge (two-hinged frame).

The next step involved developing sets of “pseudo”
pressure coefficients to generate loading conditions that
would envelop the maximum induced force components to
be resisted for all possible wind directions and exposures.
Note, for example, that the wind azimuth producing the
maximum bending moment at the knee would not
necessarily produce the maximum total uplift. The
maximum induced external force components determined
for each of the preceding five categories were used to
develop the coefficients. The end result was a set of
coefficients that represent fictitious loading conditions but
that conservatively envelop the maximum induced force

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-107

components (bending moment, shear, and thrust) to be
resisted, independent of wind direction.

The original set of coefficients was generated for the
framing of conventional pre-engineered buildings, that is,
single-storey moment-resisting frames in one of the
principal directions and bracing in the other principal
direction. The approach was later extended to single-
storey moment-resisting frames with interior columns
(Kavanagh et al. 1983).

Subsequent wind tunnel studies (isyumov and Case 1995)
have shown that the (GC p fi) values of Figure 207C.4-1 are
also applicable to low-rise buildings with structural
systems other than moment-resisting frames. That work
examined the instantaneous wind pressures on a low-rise
building with a 4:12 pitched gable roof and the resulting
wind-induced forces on its MWFRS. Two different MWFRS
were evaluated. One consisted = of shear walls and roof
trusses at different spacing. The other had moment-
resisting frames in one direction, positioned at the same
spacing as the roof trusses, and diagonal wind bracing in
the other direction. Wind tunnel tests were conducted for
both Exposures B and C. The findings of this study showed
that the (CC P/ ) values of Figure 207C.4-1 provided
satisfactory estimates of the wind forces for both types of
structural systems. This, work confirms the validity of
Figure 207C.4-1, which reflects the combined action of
wind pressures on different external surfaces of a building
and thus takes advantage of spatial averaging.

In the original wind tunnel experiments, both B and C
exposure terrains were checked. In these early
experiments, Exposure B did not include nearby buildings.
In general, the force components, bending moments, and
so forth were found comparable in both exposures,
although ( GC p f ) values associated with Exposure B
terrain would be higher than that for Exposure C terrain
because of reduced velocity pressure in Exposure B
terrain. The ( GC p f ) values given in Figures 207C.4-1,
207E.4-1, 207E.4-2A, 27E.4-2B, 27E.4-2C, 27E.4-3,
27E.4-4, 27 E. 4-5 A, 27E.4-5B, and 27 E. 4-6 are derived
from wind tunnel studies modeled with Exposure C terrain.
However, they may also be used in other exposures when
the velocity pressure representing the appropriate
exposure is used.

In comprehensive wind tunnel studies conducted by Ho at
the University of Western Ontario (1992), it was
determined that when low buildings (h < 18 m) are
embedded in suburban terrain (Exposure B, which
included nearby buildings), the pressures in most cases are
lower than those currently used in existing standards and
codes, although the values show a very large scatter
because of high turbulence and many variables. The results

seem to indicate that some reduction in pressures for
buildings located in Exposure B is justified. The ASCE
Task Committee on Wind Loads believes it is desirable to
design buildings for the exposure conditions consistent
with the exposure designations defined in the standard \ In
the case of low buildings, the effect of the increased
intensity of turbulence in rougher terrain (i.e., Exposure A
or B us’. C) increases the local pressure coefficients.
Beginning in NSCP 2001 (ASCE 7-98) the effect of the
increased turbulence intensity on the loads is treated with
the truncated profile. Using this approach, the actual
building exposure is used and the profile truncation
corrects for the underestimate in the loads that would be
obtained otherwise.

Figure 207 C. 4-1 is most appropriate for low buildings with
width greater than twice their height and a mean roof
height that does not exceed 10 m. The original database
included low buildings with width no greater than five
times their eave height, and eave height did not exceed
10m. In the absence of more appropriate data,
Figure 207C.4-1 may also be used for buildings with mean
roof height that does not exceed the least horizontal
dimension and is less than or equal to 18m. Beyond these
extended limits, Figure 207B.4-1 should be used.

All the research used to develop and refine the low-rise
building method for MWFRS loads was done on gable-
roofed buildings. In the absence of research on hip-roofed
buildings, the ASCE committee has developed a rational
method of applying Figure 207C.4-1 to hip roofs based on
its collective experience, intuition, and judgment. This
suggested method is presented in Figure C207C.4-2.

Research (Isyumov 1982 and Isyumov and Case 2000)
indicated that the low-rise method alone underestimates
the amount of torsion caused by wind loads. In
ASCE 7-02, Note 5 was added to Figure 207C.4-I to
account for this torsional effect and has been carried
forward through subsequent editions. The reduction in
loading on only 50 percent of the building results in a
torsional load case without an increase in the predicted
base shear for the building. The provision will have little
or no effect on the design of MWFRS that have well-
distributed resistance. However, it will impact the design
of systems with centralized resistance, such as a single core
in the center of the building. An illustration of the intent of
the note on two of the eight load patterns is shown in
Figure 207C.4-L All eight patterns should be modified in
this way as a separate set of load conditions in addition to
the eight basic patterns.

Internal pressure coefficients ( GC pi ) to be used for loads
on MWFRS are given in Table 207 A. 11-1. The internal
pressure load can be critical in one-storey moment-

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-108 CHAPTER 2 - Minimum Design Loads

resisting frames and in the top storey of a building where
the MWFRS consists of moment resisting frames. Loading
cases with positive and negative internal pressures should
be considered. The internal pressure load cancels out in
the determination of total lateral load and base shear. The
designer can use judgment in the use of internal pressure
loading for the MWFRS of high-rise buildings .

Figure C207C.4-1

Unsteady Wind Loads on Low Buildings for Given Wind Direction {After Ellingwood 1982)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-109

207C.4 Wind Loads — Main Wind-Force Resisting
System

207C.4.1 Design Wind Pressure for Low-Rise
Buildings

207C.4.2 Parapets

The design wind pressure for the effect of parapets on
MWFRS of low-rise buildings with flat, gable, or hip roofs
shall be determined by the following equation:

Design wind pressures for the MWFRS of low-rise
buildings shall be determined by the following equation:

P p = Q P ( GC pn ) (N/m 2 ) (207C.4-2)

P = Rh[(GC pf ) - ( GC pi )] (N/m 2 ) (207C.4-1)

where

<lh

(GC pf )

(GC pi )

velocity pressure evaluated at mean roof
height h as defined in Section 207A.3
external pressure coefficient from

Figure 207C.4-1

internal pressure coefficient from

Table 207A.11-1

207C.4.1.1 External Pressure Coefficients ( GC p f )

The combined gust effect factor and external pressure
coefficients for low-rise buildings, (GC p y), are not
permitted to be separated.

where

<Ip

(GC pn )

combined net pressure on the parapet due
to the combination of the net pressures
from the front and back parapet surfaces.
Plus (and minus) signs signify net
pressure acting toward (and away from)
the front (exterior) side of the parapet
velocity pressure evaluated at the top of
the

parapet

combined net pressure coefficient
+ 1.5 for windward parapet
-1 .0 for leeward parapet

Commentary:

Load Case A

Load Case B

Figure C207C.4-2
Hip Roofed Low-Rise Buildings

Notes:

1 . Adapt the loadings shown in Figure 207C.4-1 for hip roofed buildings as shown above. For a given hip roof pitch use the roof coefficients from the Case A table for both
Load Case A and Load Case B.

2 . The total horizontal shear shall not be less than that determined by neglecting the wind forces on roof surfaces.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

Windward

LOAD CASE A

Direction

Windward

Direction

LOAD CASE B

Windward

2-1 1 0 CHAPTER 2 - Minimum Design Loads

Figure 207C.4-1

Main Wind Force Resisting System - Part 1 External Pressure Coefficients ( GC pf )
Enclosed, Partially Enclosed Buildings, h < 18 m Low-rise Walls and Roofs

WiadwMd

Comer

Wfadwad

Basic Load Cases

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTFR 2 - Minimum Design Loads

2-111

Roof

LOAD CASE A

Angle 0

Building Surface

(degrees)

0-5

0.40

-0.69

-0.37

-0.29

0.61

-1.07

-0.53

-0.43

0.53

-0.69

-0.48

-0.43

0.80

-1.07

-0.69

-0.64

30-45

0.56

0.21

-0.43

-0.37

0.69

0.27

-0.53

-0.48

0.56

-0.37

0.69

-0.48

Roof
Angle 6
(degrees)

LOAD CASE B

Building Surface

0-90

0.45

0.69

0.37

0.45

0.4

0.29

0.48

1.07

0.53

0.48

0.61

0.43

Notes:

1 . Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

2. For values of 6 other than those shown, linear interpolation is permitted.

3. The building must be designed for all wind directions using the 8 loading patterns shown. The load patterns are applied to each building
comer in turn as the Windward Comer,

4. Combinations of external and internal pressures (see Table 207 A. 1 1-1) shall be evaluated as required to obtain the most severe loadings.

5. For the torsional load cases shown below, the pressures in zones designated with a “T” (IT, 2T, 3T, 4T, 5T, 6T) shall be 25% of the full

design wind pressures (zones 1, 2, 3, 4, 5, 6).

Exception : One storey buildings with h less than or equal to 9 m> buildings two storeys or less framed with light frame
construction , and buildings two storeys or less designed with flexible diaphragms need to be designed for the torsional load cases
Torsional loading shall apply to all eight basic load patterns using the figures below applied at each Windward Comer.

6. For purposes of designing a building’s MWFRS, the total horizontal shear shall not be less than that determined by neglecting the wind
forces on the roof.

Exception: This provision does not apply to buildings using moment frames for the MWFRS.

7. For flat roofs, use 0 = 0° and locate the zone 2/3 and zone 2E/3E boundary at the mid-width of the building.

8. The pressure coefficient ( GC p f)> when negative in Zone 2 and 2E, shall be applied in Zone 2/2E for a distance from the edge of the roof

equal 0.5 times the horizontal dimension of the building parallel to the direction of MWFRS being designed or 2.5 times the eave height
at the windward wall, whichever is less; the remainder of Zone 2/2E extending to the ridge line shall use the pressure coefficient (GC p ^)
for zone 3/3E,

9. Notation:

a: 1 0% of least horizontal dimension or . 4/i , whichever is smal ler, but not less than either 4% of least horizontal dimension or 0.9 m
h: Mean roof height, in meters, except that eave height shall be used for 9 < 10°.

6: Angle of plane of roof from horizontal, in degrees

Transverse Direction Longitudinal Direction

Torsional Load Cases

Figure 207C.4-1 (continued)

Main Wind Force Resisting System - Part l.External Pressure Coefficients
Enclosed, Partially Enclosed Buildings, h < 18m Low-rise Walls and Roofs

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-1 12 CHAPTER 2 - Minimum Design Loads

207C.4.3 Roof Overhangs

The positive external pressure on the bottom surface of
windward roof overhangs shall be determined using
C p = 0. 7 in combination with the top surface pressures
determined using Figure 207C.4-1.

207C.4.4 Minimum Design Wind Loads

Table 207C.3-1

Velocity Pressure Exposure Coefficients, K h and K z

Height above
ground level, z

Exposure

0-4.6

0.70

0.85

1.03

6.1

0.70

0.90

1.08

7.6

0.70

0.94

1.12

9.1

0.70

0.98

1.16

12.2

0.76

1.04

1.22

15.2

0.81

1.09

1.27

0.85

1.13

1.31

Notes:

I . The velocity pressure exposure coefficient K z may be
determined from the following formula:

For 4.57 m.< z < z g For z < 4.57 m

K z = 2. 01 (z/z g ) Z/ “

= 2.0l(4.57/z g ) 2/ "

Note: z shall not be taken less than 9 m in exposure B.

2. a and z g are tabulated in Table 207A.9-1.

3. Linear interpolation for intermediate values of height
z is acceptable.

4. Exposure categories are defined in Section 207A.7.

Commentary

This section specifies a minimum wind load to be applied
horizontally on the entire vertical projection of the building
as shown in Figure C207B.4-1. This load case is to be
applied as a separate load case in addition to the normal
load cases specified in other portions of this chapter.

Part 2: Enclosed Simple Diaphragm Low-Rj se
Buildings

Commentary:

This simplified approach of the Envelope Procedure is
for the relatively common low-rise (h < 18m) regular
shaped, simple diaphragm building case (see definitions
for “simple diaphragm building ” and " regular-shaped
building ”) where pressures for the roof and walls can
be selected directly from a table. Figure 207C.6-1
provides the design pressures for MWFRS for the
specified conditions. Values are provided for enclosed
buildings only ((GC pi ) = ±0.18).

Horizontal wall pressures are the net sum of the
windward and leeward pressures on vertical projection
of the wall. Horizontal roof pressures are the net sum of
the windward and leeward pressures on vertical
projection of the roof Vertical roof pressures are the net
sum of the external and internal pressures on the
horizontal projection of the roof

Note that for the MWFRS in a diaphragm building, the
internal pressure cancels for loads on the walls and for
the horizontal component of loads on the roof This is
true because when wind forces are transferred by
horizontal diaphragms (e.g., floors and roofs) to the
vertical elements of the MWFRS (e.g., shear walls, X-
bracing, or moment frames), the collection of wind
forces from windward and leeward sides of the building
occurs in the horizontal diaphragms. Once transferred
into the horizontal diaphragms by the vertically
spanning wall systems, the wind forces become a net
horizontal wind force that is delivered to the lateral
force resisting elements of the MWFRS. There should be
no structural separations in the diaphragms.
Additionally, there should be no girts or other horizontal
members that transmit significant wind loads directly to
vertical frame members of the MWFRS in the direction
under consideration. The equal and opposite internal
pressures on the walls cancel each other in the
horizontal diaphragm. This simplified approach of the
Envelope Procedure combines the windward and
leeward pressures into a net horizontal wind pressure,
with the internal pressures canceled. The user is
cautioned to consider the precise application of
windward and leeward wall loads to members of the
roof diaphragm where openings may exist and where
particular members, such as drag struts, are designed.
The design of the roof members of the MWFRS for
vertical loads is influenced by internal pressures. The
maximum uplift, which is controlled by Load Case B, is
produced by a positive internal pressure. At a roof slope

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-113

of approximately 20 and above the windward roof
pressure becomes positive and a negative internal
pressure used in Load Case 2 in the table may produce
a controlling case * From 25° to 45°, both positive and
negative internal pressure cases (Load Cases 1 and 2,
respectively) must be checked for the roof

For the designer to use this method for the design of the
MWFRS, the building must conform to all of the
requirements listed in Section 207 A. 8. 2; otherwise the
Directional Procedure, Part 1 of the Envelope
Procedure, or the Wind Tunnel Procedure must be used.
This method is based on Part 1 of the Envelope
Procedure, as shown in Figure 2 07 C. 4-1, for a specific
group of buildings (simple diaphragm buildings).
However, the torsional loading from Figure 2 07 C .4-1 is
deemed to be too complicated for a simplified method.
The last requirement in Section 207C.6.2 prevents the
use of this method for buildings with lateral systems that
are sensitive to torsional wind loading.

Note 5 of Figure 207 C. 4-1 identifies several building
types that are known to be insensitive to torsion and may
therefore be designed using the provisions of
Section 207C.6. Additionally, buildings whose lateral
resistance in each principal direction is provided by two
shear walls, braced frames, or moment frames that are
spaced apart a distance not less than 75 percent of the
width of the building measured normal to the orthogonal
wind direction, and other building types and element
arrangements described in Section 207B.6.1 or
207B.6.2 are also insensitive to torsion. This property
could be demonstrated by designing the building using
Part 1 of Section 207C, Figure 207C.4-1, and showing
that the torsion load cases defined in Note 5 do not
govern the design of any of the lateral resisting
elements. Alternatively, it can be demonstrated within
the context of Part 2 of Section 207 C by defining torsion
load cases based on the loads in Figure 207C.6-1 and
reducing the pressures on one-half of the building by 75
percent, as described in Figure 207 C. 4-1, Note 5. If
none of the lateral elements are governed by these
torsion cases, then the building can be designed using
Part 2 of Section 207C; otherwise the building must be
designed using Part 1 of Section 207B or Part 1 of
Section 207 C.

Values are tabulated for Exposure B at h = 9.0 m, and
K zt = 1.0. Multiplying factors are provided for other
exposures and heights. The following values have been
used in preparation of the figures:

Exposure B

(GCpi)

= ±0.18 (enclosed building)

= 9.0 m

K d

= 0.85

K z = 0. 70

K zt = TO

Pressure coefficients are from Figure 207C.4-T

Wall elements resisting two or more simultaneous wind-
induced structural actions (e.g., bending, uplift, or
shear) should be designed for the interaction of the wind
loads as part of the MWFRS. The horizontal loads in
Figure 207C.6-1 are the sum of the windward and
leeward pressures and are therefore not applicable as
individual wall pressures for the interaction load cases.
Design wind pressures, p s for zones A and C, should be
multiplied by + 0.85 for use on windward walls and by -
0.70 for use on leeward walls (the plus sign signifies
pressures acting toward the wall surface). For side
walls, p s for zone C multiplied by - 0.65 should be used.
These wall elements must also be checked for the
various separately acting (not simultaneous) component
and cladding load cases.

Main wind-force resisting roof members spanning at
least from the eave to the ridge or supporting members
spanning at least from eave to ridge are not required to
be designed for the higher end zone loads. The interior
zone loads should be applied. This is due to the
enveloped nature of the loads for roof members.

207C.5 General Requirements

The steps required for the determination of MWFRS wind
loads on enclosed simple diaphragm buildings are shown
in Table 207C.5-1.

User Note:

Part 2 of Section 207 C is a simplified method to
determine the wind pressure on the MWFRS of enclosed
simple diaphragm low-rise buildings having a flat,
gable or hip roof. The wind pressures are obtained
directly from a table and applied on horizontal and
vertical projected surfaces of the building. This method
is a simplification of the Envelope Procedure contained
in Part 1 of Section 207 C.

207C.5.1 Wind Load Parameters Specified in Section
207A

The following wind load parameters are specified in
Section 207A:

• Basic Wind Speed V (Section 207A.5)

• Exposure category (Section 207A.7)

Philippines Volume I, 7th Edition, 2015

National Structural Code of the

2-114 CHAPTER 2 - Minimum Design Loads

• Topographic factor K zt (Section 207A.8)

• Enclosure classification (Section 207A.10)

Table 207C.5-1

Steps to Determine Wind Loads on MWFRS Simple
Diaphragm Low-Rise Buildings

Step 1 : Determine occupancy category of building or
other structure, see Table 103-1

Step 2: Determine the basic wind speed, V, for the
applicable risk category, see Figure 207A.5-
1A, B or C

Step 3: Determine wind load parameters:

> Exposure category B, C or D, see
Section 207A.7

> Topographic factor, K zt , see Section
207A.8 and Figure 207A.8-1

Step 4; Enter figure to determine wind pressures for
h = 9 m, Ps 3 o, see Figure 207C.6-1

Step 5: Enter figure to determine adjustment for
building height and exposure, A, see
Figure 207C.6-1

Step 6: Determine adjusted wind pressures, p s , see
Equation 207C.6-1

207C.6 Wind Loads - Main Wind-Force Ruskm

System ^

207C.6.1 Scope

A building whose design wind loads are determined i
accordance with this section shall meet all the condition!
of Section 207C.6.2. If a building does not meet all of the
conditions of Section 207C.6.2, then its MWFRS wind
loads shall be determined by Part 1 of this chapter, by ^
Directional Procedure of Section 207B, or by the Wind
Tunnel Procedure of Section 207F.

207C.6.2 Conditions

For the design of MWFRS the building shall comply with
all of the following conditions:

1 * The building is a simple diaphragm building as
defined in Section 207A.2.

2. The building is a low-rise building as defined in
Section 207A.2.

3. The building is enclosed as defined in Section 207A.2
and conforms to the wind-borne debris provisions of
Section 207A.10.3.

4. The building is a regular-shaped building or structure
as defined in Section 207A.2.

5. The building is not classified as a flexible building as
defined in Section 207A.2.

6. The building does not have response characteristics
making it subject to across wind loading, vortex
shedding, instability due to galloping or flutter; and it
does not have a site location for which channeling
effects or buffeting in the wake of upwind obstructions
warrant special consideration.

7. The building has an approximately symmetrical cross-
section in each direction with either a flat roof or a
gable or hip roof with 0 < 45 ° .

8. The building is exempted from torsional load cases as
indicated in Note 5 of Figure 207C.4-1, or the torsional
load cases defined in Note 5 do not control the design
of any of the MWFRS of the building.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-1 15
$.

207C.6.3 Design Wind Loads

Simplified design wind pressures, p s , for the MWFRS of
low-rise simple diaphragm buildings represent the net
pressures (sum of internal and external) to be applied to the
horizontal and vertical projections of building surfaces as
shown in Figure 207C.6-1. For the horizontal pressures
(Zones A, B, C, D), p s is the combination of the windward
and leeward net pressures. p s shall be determined by the
following equation:

207C.6.4 Minimum Design Wind Loads

The load effects of the design wind pressures from Section
207C.6.3 shall not be less than a minimum load defined by
assuming the pressures, p s , for zones A and C equal to
+766 Pa, Zones B and D equal to +383 Pa, while assuming
p s for Zones E, F, G, and H are equal to 0.0 Pa.

Ps — A.KztPs30 (207C.6-1)

where

A adjustment factor for building height and

exposure from Figure 207C.6-1

K zt topographic factor as defined in

Section 207A.8 evaluated at mean roof
height, h

p S3Q simplified design wind pressure for

Exposure B, at h = 9 m from Figure 207 C. 6-
1

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-116 CHAPTER 2 - Minimum Design Loads

Notes:

1 . Pressures shown are applied to the horizontal and vertical projections, for exposure B, at h = 9 m. Adjust to other exposures and height
with adjustment factor X.

2. The load patterns show shall be applied to each comer of the building in turn as the reference comer. (See Figure 207C.4-1)

3. For Case B use 9 = 0°.

4. Load cases 1 and 2 must be checked for 25° < 6 < 45°, Load case 2 at 25° is provided only for interpolation between 25° and 30°.

5. Plus and minus signs signify pressures acting toward and away from the projected surfaces, respectively.

6. For roof slopes other than those shown, linear interpolation is permitted.

7. The total horizontal load shall not be less than that determined by assuming p s = 0 in zones B and D.

8. Where zone E or G falls on a roof overhang on the windward side of the building, use E 0H and G 0H for the pressure on the horizontal

projection of the overhang. Overhangs on the leeward and side edges shall have the basic zone pressure applied.

9. Notation:

a : 10% of least horizontal dimension or 0.4/i, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m
h : Mean roof height, in meters, except that eave height shall be used for roof angles < 10°.

0: Angle of plane of roof from horizontal, in degrees.

Figure 207C.6-1

Main Wind Force Resisting System - Method 2.Design Wind Pressure
Enclosed Buildings h < 18 m Walls and Roofs

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-1 1 7

rr pijsif

Wind

Speed

Roof

Angle

(degrees)

Load

Case

Zones

Horizontal Pressures

Vertical Pressures

Overhangs

EOH

GOH

150

0 to 5°

0.66

-0.34

0.44

-0.2

-0.79

-0.45

-0.55

-0.35

-1.11

-0.87

10°

0.74

-0.31

0.49

-0.18

-0.79

-0.48

-0.55

-0.37

-1.11

-0.87

15°

0.83

-0.27

0.55

-0.16

-0.79

-0.52

-0.55

-0.39

-1.11

-0.87

0.91

-0.24

0.61

-0.13

-0.79

-0.55

-0.42

-1.11

-0.87

25°

0.83

0.13

0.6

0.14

-0.37

-0.5

-0.27

-0.41

-0.68

-0.58

1 -0.14

-0.27

-0.04

-0.18

30 to 45°

0.74

0.51

0.59

0.41

0.06

-0.45

0.02

-0.39

-0,26

-0.3

0.74

0.51

0.59

0.41

0.29

-0.22

0.25

-0.16

-0.26

-0.3

200

L/l

1.17

-0.61

0.78

-0.36

-1.41

-0.8

-0.98

-0.62

-1.97

-1.54

10°

1.32

-0.55

0.88

-0.32

-1.41

-0.86

-0.98

-0.67

-1.97

-1.54

15°

1.48

-0.48

0.98

-0.28

; -1.41

-0.92

-0.98

-0.7

-1.97

-1.54

20°

1.62

-0.43

1.08

-0.23

-1.41

-0.98

-0.74

-1.97

-1.54

25°

1.48

0.23

1.07

0.25

-0.65

-0.89

-0.47

-0.72

-1.22

-1.03

-0.25

-0.48

-0.07

-0.32

30 to 45°

1.32

0.9

1.05

0.72

0.1

-0.8

0.03

-0.68

-0.46

-0.53

1.32

0.9

1.05

0.72

0.51

-0.39

0.44

-0.28

-0.46

-0.53

250

1.83

-0.95

1.22

-0.57

-2.2

-1.25

-1.53

-0.97

-3.08

-2.41

10°

2.06

-0.86

1.37

-0.49

-2.2

-1.34

-1.53

-1.04

-3.08

-2.41

15°

2.31

-0.76

1.53

-0.44

-2.2

-1.44

-1.53

-1.09

-3.08

-2.41

20°

2.53

-0.67

1.69

-0.37

-2.2

-1.53

-1.16

-3.08

-2.41

25°

2.31

0.37

1.67

0.39

-1.02

-1.39

-0.74

-1.13

-1.9

-1.62

-0.39

-0.76 '

-0.11

-0.49

30 to 45°

2.06

1.41

1.64

1.13

0.16

-1.25

0.05

-1.07

-0.72

-0.83

2.06

1.41

1.64

1.13

0.79

-0.62

0.68

-0.44

-0.72

-0.83

Figure 207C.6-1

Main Wind Force Resisting System - Method 2 Design Wind Pressure
Enclosed Buildings h < 18 m Walls and Roofs, Simplified Design Wind Pressure, p S9 0 (Pa)

(Exposure B at h = 9.0 m with 7=1.0

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-118 CHAPTER 2 - Minimum Design Loads

Basic

Wind

Speed

(kph)

Roof

Angle

(degrees)

Zones

Load

Case

Horizontal Pressures

Vertical Pressures

Overhanes

EOH

COH

0 to 5°

2.63

-1.37

1.75

-0.81

-3.17

-1.8

-2.2

-1.39

-4.44

-3.47 '

10°

2.97

-1.24

1.98

-0.71

-3.17

-1.93

-2.2

-1.49

-4.44

-3.47

300

15°

3.32

-1.09

2.2

-0.63

-3.17

-2.08

-2.2

-1.57

-4.44

-3.47

20°

3.65

-0.96

2.43

-0.53

-3.17

-2.2

-1.67

-4.44

-3.47

25°

3.32

0.53

2.41

0.56

-1.47

-2

-1.06

-1.62

-2.74

-2.33

-0.56

-1.09

-0.15

-0.71

30 to 45°

2.97

2.03

2.36

1.62

0.23

-1.8

0.08

-1.55

-1.04

-1.19

2.97

2.03

2.36

1.62

1.14

-0.89

0.99

-0.63

-1.04

-1.19

350

0 to 5°

3.59

-1.86

2.38

-1.11

-4.32

-2.45

-3

-1.9

-6.04

-4.73

10°

4.04

-1.69

2.69

-0.97

-4.32

-2.62

-3

-2.04

-6.04

-4.73

15°

4.52

-1.48

-0.86

-4.32

-2.83

-3

-2.14

-6.04

-4.73 1

4.97

-1.31

3.31

-0.72

-4.32

-3

-2.28

-6.04

-4.73

25°

4.52

0.72

3.28

0.76

-2

-2.73

-1.45

-2.21

-3.73

-3.18

-0.76

-1.48

-0.21

-0.97

30 to 45°

4.04

2.76

3.21

, 2.21

0.31

-2.45

0.11

-2.1

-1.41

-1.62 1

4.04

2.76

3.21

2.21

1.55

-1.21

1.35

-0.86

-1.41

-1.62

Adjustment Factor for Building Height and Exposure, A

Mean Roof
Height (m)

Exposure

0-5

1.0

1.21

1.47

1.0

1.29

1.55

1.0

1.35

1.61.

1.0

1.40

1.66

1.05

1.45

1.70

1.09

1.49

1.74

1.12

1.53

1.78

1.16

1.56

1.81

1.19

1.59

1.84

1.22

1.62

1.87

Figure 207C.6-1 (continued)

Main Wind Force Resisting System - Method 2 Design Wind Pressure
Enclosed Buildings h < 18 m Walls and Roofs, Simplified Design Wind Pressure, p S9 . o ( Pa )

(Exposure B at h = 9.0 m with / = 1 .0

Association of Structural Engineers of the Philippines, Inc. (ASEP)

2-119

CHAPTER 2 - Minimum Design Loads

207D Wind Loads on Other Structures and Building
Appurtenances - MWFRS

207D.1 Scope

207D.1.1 Structure Types

This section applies to the determination of wind loads on
building appurtenances (such as rooftop structures and
rooftop equipment) and other structures of all heights (such
as solid freestanding walls and freestanding solid signs,
chimneys, tanks, open signs, lattice frameworks, and
trussed towers) using the Directional Procedure.

The steps required for the determination of wind loads on
building appurtenances and other structures are shown in
Table 207D.1-1.

User Note:

Use Section 207D to determine wind pressures on the
MWFRS of solid freestanding walls, freestanding solid
signs, chimneys, tanks, open signs, lattice frameworks
and trussed towers. Wind loads on rooftop structures
and equipment may be determined from the provisions
of this chapter. The wind pressures are calculated using
specific equations based upon the Directional
Procedure.

207D.1.2 Conditions

A structure whose design wind loads are determined in
accordance with this section shall comply with all of the
following conditions:

1. The structure is a regular-shaped structure as defined
in Section 207A.2.

2, The structure does not have response characteristics
making it subject to across-wind loading, vortex
shedding, or instability due to galloping or flutter; or it
does not have a site location for which channeling
effects or buffeting in the wake of upwind obstructions
warrant special consideration.

207D.1.3 Limitations

The provisions of this chapter take into consideration the
load magnification effect caused by gusts in resonance with
along-wind vibrations of flexible structures. Structures not
meeting the requirements of Section 207D.1.2, or having
unusual shapes or response characteristics, shall be

designed using recognized literature documenting such
wind load effects or shall use the Wind Tunnel Procedure
specified in Section 207F.

207D.1.4 Shielding

There shall be no reductions in velocity pressure due to
apparent shielding afforded by buildings and other
structures or terrain features.

207D.2 General Requirements

207D.2.1 Wind Load Parameters Specified in
Section 207A

The following wind load parameters shall be determined in
accordance with Section 207A:

• Basic Wind Speed V (Section 207A.5)

• Wind directionality Factor K d (Section 207A.6)

• Exposure category (Section 207A.7)

• Topographic factor K zt (Section 207A.8)

• Enclosure classification (Section 207 A. 1 0)

207D.3 Velocity Pressure

207D.3.1 Velocity Pressure Exposure Coefficient

Based on the exposure category determined in
Section 207A.7.3, a velocity pressure exposure coefficient
K z or K h , as applicable, shall be determined from
Table 207D.3-1.

For a site located in a transition zone between exposure
categories that is near to a change in ground surface
roughness, intermediate values of K z or K h , between those
shown in Table 207D.3-1, are permitted, provided that they
are determined by a rational analysis method defined in the
recognized literature.

Commentary :

See commentary, Section C207B.3.L

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-120 CHAPTER 2 - Minimum Design Loads

207D.3.2 Velocity Pressure

Velocity pressure, q z , evaluated at height z shall be
calculated by the following equation:

Table 207D.1-1

Steps to Determine Wind Loads on MWFRS Rooftop
Equipment and Other Structures

Step 1 : Determine occupancy category of building or
other structure, see Table 103-1

Step 2: Determine the basic wind speed, V , for the

applicable risk category, see Figure 207A.5-

where

1A, B or C

K d = wind directionality factor, see

Section 207A.6

K z = velocity pressure exposure

coefficient, see Section 207D.3.1
K zt = topographic factor defined, see

Section 207A.8.2

Step 3: Determine wind load parameters:

> Wind directionality factor, K d , see
Section 207A.6 and Table 207A.6-1

> Exposure category B, C or D, see
Section 207A.7

V — basic wind speed, see Section 207A.5

q h = velocity pressure calculated using

Equation 207D.3-1 at height h

> Topographic factor, K zt , see

Section 207A.8 and Figure 207A.8-1

The numerical coefficient 0.613 shall be used except
where sufficient climatic data are available to justify the
selection of a different value of this factor for a design
application.

> Gust Effect Factor, G , see Section 207A.9

Step 4: Determine velocity pressure exposure

coefficient, K z or see Table 207D.2-1

Step 5: Determine velocity pressure q z or see
Equation 207D.3-1

Step 6: Determine force coefficient, Cf

> Solid freestanding signs or solid
freestanding walls, Figure 207D.4-1

> Chimneys, tanks, rooftop equipment
Figure 207D.5-1

> Open signs, lattice frameworks
Figure 207D.5-2

> Trussed towers Figure 207D.4-3
Step 7: Calculate wind force, F :

> Equation 207D.4-1 for signs and walls

> Equation 207D.6-1 and Equation 207D.6-
2 for rooftop structures and equipment

> Equation 207D.5-1 for other structures

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-121

Commentary :

See commentary, Section C207B.3.2.

Figure 207D.4-1. The force coefficients for solid
freestanding walls and signs in Figure 207D.4-1 date
back to ANSI A58. 1-1972. It was shown by Letchford
(2001) that these data originated from wind tunnel
studies performed by Flachsbart in the early 1930s in
smooth uniform flow . The current values in Figure
207 D. 4-1 are based on the results of boundary layer
wind tunnel studies (Letchford 1985, 2001, Holmes
1986, Letchford and Holmes 1994, Ginger et ai 1998a
and 1998b, and Letchford and Robertson 1999).

A surface curve fit to Letchford's (2001) and Holmes's
( 1 986) area averaged mean net pressure coefficient data
(equivalent to mean force coefficients in this case) is
given by the following equation

( 1. 563 + 0. 0042 InO ) - 0. 06148y > j
C f = j +0. 009011[ln(x)] 2 — 0. 2603y 2 t/o.8
( — 0. 08393y[ln(jt)] )

where x — B/s and y — s/h

The 0.85 term in the denominator modifies the wind
tunnel-derived force coefficients into a format where the
gust effect factor as defined in Section 207A.9 can be
used.

Force coefficients for Cases A and B were generated
from the preceding equation, then rounded off to the
nearest 0.05. That equation is only valid within the
range of B/s and s/h ratios given in the figure for Case
A and B.

Of all the pertinent studies, only Letchford (2001)
specifically addressed eccentricity (i.e., Case B).
Letchford reported that his data provided a reasonable
match to Cook's (1990) recommendation for using an
eccentricity of 0.25 times the average width of the sign.
However, the data were too limited in scope to justify
changing the existing eccentricity value of 0.2 times the
average width of the sign, which is also used in the latest
Australian / New Zealand Standard (Standards
Australia 2002).

Case C was added to account for the higher pressures
observed in both wind tunnel (Letchford 1985, 2001,
Holmes 1986, Letchford and Holmes 1994, Ginger et al.
1998a and 1998b, and Letchford and Robertson 1999)
and full-scale studies (Robertson et al. 1997) near the
windward edge of a freestanding wall or sign for oblique
wind directions. Linear regression equations were fit to

the local mean net pressure coefficient data (for wind
direction 45°) from the referenced wind tunnel studies
to generate force coefficients for square regions starting
at the windward edge. Pressures near this edge increase
significantly as the length of the structure increases. No
data were available on the spatial distribution of
pressures for structures with low aspect ratios (B/s <
2 ).

The sample illustration for Case C at the top of
Figure 207D.4-1 is for a sign with an aspect ratio
B/s = 4. For signs of differing B/s ratios, the number
of regions is equal to the number of force coefficient
entries located below each B/s column heading.

For oblique wind directions (Case C), increased force
coefficients have been observed on aboveground signs
compared to the same aspect ratio walls on ground
(Letchford 1985, 2001 and Ginger et al 1998a). The
ratio of force coefficients between above-ground and
on-ground signs (i.e., s/h = 0. 8 and 1.0, respectively)
is 1.25, which is the same ratio used in the Australian /
New Zealand Standard (Standards Australia 2002).
Note 5 of Figure 207D.4-1 provides for linear
interpolation between these two cases.

For walls and signs on the ground (s/h = 1), the mean
vertical center of pressure ranged from 0. 5Ai to 0. 6 h
(Holmes 1986, Letchford 1989, Letchford and Holmes
1994, Robertson et al. 1995, 1996, and Ginger et al.
1998a) with 0. 55ft being the average value. For
above-ground walls and signs, the geometric center best
represents the expected vertical center of pressure.

The reduction in Cf due to porosity (Note 2) follows a
recommendation (Letchford 2001). Both wind tunnel
and full-scale data have shown that return corners
significantly reduce the net pressures in the region near
the windward edge of the wall or sign (Letchford and
Robertson 1999).

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-122 CHAPTER 2 - Minimum Design Loads

207D.4 Design Wind Loads - Solid Freestanding Walls
and Solid Signs

207D.4.1 Solid Freestanding Walls and Solid
Freestanding Signs

The design wind force for solid freestanding walls and
solid freestanding signs shall be determined by the
following formula:

F = q h GC f A s (N) (207D.4-1)

where

q h = velocity pressure evaluated at height h
(defined in Figure 207D.4-1) as determined
in accordance with Section 207D.3.2

G = gust-effect factor from Section 207 A.9
Cf = net force coefficient from Figure 207D.4-1

A s = the gross area of the solid freestanding wall

or freestanding solid sign, m 2

207D.4.2 Solid Attached Signs

The design wind pressure on a solid sign attached to the
wall of a building, where the plane of the sign is parallel to
and in contact with the plane of the wall, and the sign does
not extend beyond the side or top edges of the wall, shall
be determined using procedures for wind pressures on
walls in accordance with Section 207E, and setting the
internal pressure coefficient (GC p 0 equal to 0.

This procedure shall also be applicable to solid signs
attached to but not in direct contact with the wall, provided
the gap between the sign and wall is no more than 0.9 m
and the edge of the sign is at least 0.9 m in from free edges
of the wall, i.e., side and top edges and bottom edges of
elevated walls.

Commentary:

Signs attached to walls and subject to the geometric
limitations of Section 207D.4.2 should experience wind
pressures approximately equal to the external pressures on
the wall to which they are attached. The dimension
requirements for signs supported by frameworks, where
there is a small gap between the sign and the wall, are
based on the collective judgment of the committee.

Figures 207D.5-1, 207D.5-2 and 207D.5-3. With the
exception of Figure 207D.5-3, the pressure and force
coefficient values in these tables are unchanged from ANSI
A58. 1-1972. The coefficients speeijied in these tables are
based on wind-tunnel tests conducted under conditions of
uniform flow and low turbulence, and their validity in

turbulent boundary-layer flows has yet to be completely
established. Additional pressure coefficients for conditions
not specified herein may be found in two references (SIA
1956 and ASCE 1961).

With regard to Figure 207D.5-3. the force coefficients are
a refinement of the coefficients specified in ANSI A 58. 1-
1982 and in ASCE 7-93. The force coefficients specified
are offered as a simplified procedure that may be used for
trussed towers and are consistent with force coefficients
given in ANSI/EIA/TIA-222 E-I99I. Structural Standards
for Steel Antenna Towers and Antenna Supporting
Structures, and force coefficients recommended by
Working Group No. 4 (Recommendations for Guyed
Masts), International Association for Shell and Spatial
Structures (1981).

It is not the intent of this code to exclude the use of other
recognized literature for the design of special structures,
such as transmission and telecommunications towers.
Recommendations for wind loads on tower guys are not
provided as in previous editions of the code. Recognized
literature should be referenced for the design of these
special structures as is noted in Section 207D. 1 .3. lor the
design of flagpoles, see ANSI/ NAA M M FF 1001-97. 4th
Ed.. Guide Specifications for Design of Metal Flagpoles.

207D.5 Design Wind Loads — Other Structures

The design wind force for other structures (chimneys,
tanks, rooftop equipment for h > 60 ° , and similar
structures, open signs, lattice frameworks, and trussed
towers) shall be determined by the following equation:

F = q z GC f A f (N) (207D.5-1)

where

q z = velocity pressure evaluated at height z as
defined in Section 207D.3, of the centroid
of area A f

G = gust-effect factor from Section 207A.9
Cf = force coefficients from Figures 207D.5-1
through 207D.5-3

A s = projected area normal to the wind except
where Cf is specified for the actual surface
area, m 2

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 Minimum Design Loads 2-123

207D.5.1 Rooftop Structures and Equipment for

Buildings with h < 18 m

The lateral force F h on rooftop structures and equipment
located on buildings with a mean roof height h < 18 in
shall be determined from Equation 207D.5-2.

F h = q h {GCy)Af (N) (207D.5-2)

where

(GC r ) = 1.9 for rooftop structures and equipment

with A f less than (0. 1 Bh). ( GCr ) shall be
permitted to be reduced linearly from 1.9
to 1.0 as the value of Af is increased from

(0. 1 Bh) to (Bh)

q k = velocity pressure evaluated at mean roof
height of the building

Af = vertical projected area of the rooftop
structure or equipment on a plane normal
to the direction of wind, m 2

The vertical uplift force, F v , on rooftop structures and
equipment shall be determined from Equation 207D.5-3.

F v = q h (GC r )A r (N) (207D.5-3)

Where

(GC r ) = 1.5 for rooftop structures and equipment

with A r less than (0. 1 BL). (GC r ) shall be
permitted to be reduced linearly from 1.5
to 1.0 as the value of A r is increased from

(0. 1 BL) to (BL)

q h = velocity pressure evaluated at mean roof
height of the building

Af = horizontal projected area of rooftop
structure or equipment, m 2

Commentary:

This code requires the use of Figure 207D.5-1 for the
determination of the wind force on small structures and
equipment located on a rooftop . Because of the small size
of the structures in comparison to the building, it is
expected that the wind force will be higher than predicted
by Equation 207D.6-1 due to higher correlation of
pressures across the structure surface, higher turbulence
on the building roof, and accelerated wind speed on the
roof

A limited amount of research is available to provide better
guidance for the increased force (Hosoya et al 2001 and
Kopp and Traczuk 2008). Based on this research, the force
of Equation 207D.6-1 should be increased for units with

areas that are relatively small with respect to that of the
buildings they are on. Because GC r is expected to
approach 1.0 as Af or A r approaches that of the building
(Bh or BL), a linear interpolation is included as a way to
avoid a step function in load if the designer wants to treat
other sizes. The research in Hosoya et al (2001) only
treated one value of Af (0. 04Bh). The research in Kopp
and Traczuk (2008) treated values of Af = 0.02 Bh and
0.03Bh, and values of A r = 0. 0061 BL.

In both cases the research also showed high uplifts on the
top of rooftop. Hence uplift load should also be considered
by the designer and is addressed in Section 207D.6.

207D.6 Parapets

Wind loads on parapets are specified in Section 207B.4.5
for buildings of all heights designed using the Directional
Procedure and in Section 207C.4.2 for low-rise buildings
designed using the Envelope Procedure.

Commentary:

Prior to the 2002 edition of the standard, no provisions for
the design of parapets had been included due to the lack of
direct research. In the 2002 edition of this standard, a
rational method was added based on the committee's
collective experience, intuition, and judgment. In the 2005
edition, the parapet provisions were updated as a result of
research performed at the University of Western Ontario
(Mans et al. 2000, 2001) and at Concordia University
(Stathopoulos et al. 2002a, 2002b).

Wind pressures on a parapet are a combination of wall and
roof pressures, depending on the location of the parapet
and the direction of the wind (Figure C207D.7-1). A
windward parapet will experience the positive wall
pressure on its front surface (exterior side of the building)
and the negative roof edge zone pressure on its back
surface (roof side). This behavior is based on the concept
that the zone of suction caused by the wind stream
separation at the roof eave moves up to the top of the
parapet when one is present. Thus the same suction that
acts on the roof edge will also act on the back of the
parapet.

The leeward parapet will experience a positive wall
pressure on its back surface (roof side) and a negative wall
pressure on its front surface (exterior side of the building).
There should be no reduction in the positive wall pressure
to the leeward parapet due to shielding by the windward
parapet because, typically, they are too far apart to
experience this effect. Because all parapets would be
designed for all wind directions, each parapet would in

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-124 CHAPTER 2 - Minimum Design Loads

turn be the windward and leeward parapet and \ therefore,
must be designed for both sets of pressures.

For the design of the MWFRS, the pressures used describe
the contribution of the parapet to the overall wind loads on
that system. For simplicity, the front and backpressures on
the parapet have been combined into one coefficient for
MWFRS design. The designer should not typically need the
separate front and back pressures for MWFRS design. The
internal pressures inside the parapet cancel out in the
determination of the combined coefficient. The summation
of these external and internal, front and back pressure
coefficients is a new term GC pn , the Combined Net
Pressure Coefficient for a parapet.

For the design of the components and cladding, a similar
approach was used. However, it is not possible to simplify
the coefficients due to the increased complexity of the
components and cladding pressure coefficients. In
addition, the front and back pressures are not combined
because the designer may be designing separate elements
on each face of the parapet . The internal pressure is
required to determine the net pressures on the windward
and leeward surfaces of the parapet. The provisions guide
the designer to the correct GC p and velocity pressure to
use for each surface, as illustrated in Figure C207D.7-1.
Interior walls that protrude through the roof, such as party
walls and fire walls, should be designed as windward
parapets for both MWFRS and components and cladding.

The internal pressure that may be present inside a parapet
is highly dependent on the porosity of the parapet envelope.
In other words, it depends on the likelihood of the wall
surface materials to leak air pressure into the internal
cavities of the parapet. For solid parapets, such as
concrete or masonry, the internal pressure is zero because
there is no internal cavity. Certain wall materials may be
impervious to air leakage , and as such have little or no
internal pressure or suction, so using the value of GC pi for
an enclosed building may be appropriate. However,
certain materials and systems used to construct parapets
containing cavities are more porous, thus justifying the use
of the GC pi values for partially enclosed buildings, or
higher. Another factor in the internal pressure
determination is whether the parapet cavity connects to the
internal space of the building, allowing the building's
internal pressure to propagate into the parapet. Selection
of the appropriate internal pressure coefficient is left to the
judgment of the design professional.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-125

imnil Hd iBUtiil Piraoet Prewrtt

(Uwyo tw n U indLTlJdfig Uidy)

Figure C207D.7-1
Design Wind Pressures on Parapets

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-126 CHAPTER 2 - Minimum Design Loads

207D.7 Roof Overhangs

Wind loads on roof overhangs are specified in
Section 207B.4.4 for buildings of all heights designed
using the Directional Procedure and in Section 207C.4.3
for low-rise buildings designed using the Envelope
Procedure.

207D.8 Minimum Design Wind Loading

The design wind force for other structures shall be not less
than 0.77 kN/m 2 multiplied by the area Af.

Table 207D.3-1 Velocity Pressure Exposure Coefficients, Kh and K z

Height above ground
level, z (meters)

Exposure

0-4.5

0.572

0.846

1.027

6.0

0.621

0.899

1.080

7.5

0.662

0.942

1.123

9.0

0.697

0.979

1.159

12.0

0.757

1.040

1.218

15.0

0.807

1.090

1.267

18.0

0.850

1.133

1.307

21.0

0.888

1.170

1.343

24.0

0.923

1.204

1.375

27.0

0.955

1.234

1.403

30.0

0.984

1.261

1.429

36.0

1.036

1.311

1.475

42.0

1.083

1.354

1.515

48.0

1.125

1.393

1.551

54.0

1.164

1.428

1.583

60.0

1.199

1.460

1.612

75.0

1.278

1.530

1.676

90.0

1.347

1.590

1.730

105.0

1.407

1.642

1.777

120.0

1.462

1.689

1.819

135.0

1.512

1.731

1.856

150.0

1.558

1.770

1.891

Notes:

1 . The velocity pressure exposure coefficient K z may be determined from the following formula:
For 4.5 m< z < z g For z <4.5 m

K z = 2. 01 (z/z g ) 2/ “ K z = 2 . 01 ( 4 . 57/z g ) V “

Commentary >:

This section specifies a minimum wind load to be ctppftyM
horizontally on the entire vertical projection of the building
or other structure, as shown in Figure C207B.4-L This
load case is to be applied as a separate load case
addition to the normal load cases specified in other
portions of this chapter.

2. The constants a and z g are tabulated in Table 207A.9-1 .

3. Linear interpolation for intermediate values of height z is permitted.

4. Exposure categories are defined in Section 207A.7.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

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Notes:

1 . The term "signs" in notes below also applies to "freestanding walls".

2. Signs with openings comprising less than 30% of the gross area are classified as solid signs. Force coefficients for solid signs with
openings shall be permitted to be multiplied by the reduction factor (1 — (1 — e) 15 ).

3. To allow for both normal and oblique wind directions, the following cases shall be considered:

For s/h < 1:

CASE A: resultant force acts normal to the face of the sign through the geometric center.

CASE B: resultant force acts normal to the face of the sign at a distance from the geometric center toward the windward
edge equal to 0.2 times the average width of the sign.

For B/s > 2, CASE C must also be considered:

CASE C: resultant forces act normal to the face of the sign through the geometric centers of each region.

For s/h = 1:

The same cases as above except that the vertical locations of the resultant forces occur at a distance above the geometric
center equal to 0.05 times the average height of the sign.

4. For CASE C where s/h > 0.8, force coefficients shall be multiplied by the reduction factor (1. 8 — s/h).

5. Linear interpolation is permitted for values of s/h, B/s and L r /s other than shown.

6. Notation:

B: horizontal dimension of sign, m; e : ratio of solid area to gross area;

h: height of the sign, m L r \ horizontal dimension of return comer, m

s : vertical dimension of the sign, m;

Figure 207D.4-1

Design Wind Loads Force Coefficients ( Cf ) Other Structures
All Heights of Solid Freestanding Walls & Solid Freestanding Signs

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-128 CHAPTER 2 - Minimum Design Loads

1 . The design wind force shall be calculated based on the area of the structure projected on a plane normal to the wind direction. The
force shall be assumed to act parallel to the wind direction.

2. Linear interpolation is permitted for h/D values other than shown.

3. Notation:

D: diameter of circular cross-section and least horizontal dimension of square, hexagonal or octagonal cross-sections at elevation
under consideration, in meters;

D': depth of protruding elements such as ribs and spoilers, m; and
h : height of structure, m; and

q z \ velocity pressure evaluated at height z above ground, N/m 2

4. For rooftop equipment on buildings with a mean roof height of h < 18 m, use Section 207D.5. 1 .

Figure 207D.5-1

Other Structures Force Coefficients, Cf
Chimneys, Tanks, Rooftop Equipment, & Similar Structures

ez.

Flat-Sided

Rounded Members

Members

Djq~ z < 5.3

Djq~ z > 5.3

<0.1

2.0

1.2

0.8

0.1 to 0.29

1.8

1.3

0.9

0.3 to 0.7

1.6

1.5

1.1

Notes:

1. Signs with openings comprising 30% or more of the gross area are classified as open signs.

2. The calculation of the design wind forces shall be based on the area of all exposed members and elements projected on a plane
normal to the wind direction. Forces shall be assumed to act parallel to the wind direction.

3. The area Af consistent with these force coefficients is the solid area projected normal to the wind direction.

4. Notation:

e\ ratio of solid area to gross area;

D: diameter of a typical round member, m;

q z : velocity pressure evaluated at height z above ground, N/m 2

Figure 207D.5-2

Other Structures Force Coefficients, C f All Heights of Open Signs & Lattice Frameworks

Association of Structural Engineers of the Philippines, Inc, (ASEP)

CHAPTER 2 - Minimum Design Loads 2-129

Tower Cross Section

Square

4. Oe 2 -5.9e +4.0

Triangle

3.4e 2 — 4. 7e + 3.4

Notes:

1 . For all wind directions considered, the area Af consistent with the specified force coefficients shall be the solid area of a tower face
projected on the plane of that face for the tower segment under consideration,

2. The specified force coefficients are for towers with structural angles or similar flat sided members.

3. For towers containing rounded members, it is acceptable to multiply the specified force coefficients by the following factor when
determining wind forces on such members:

0. 51e 2 + 0. 57, but not > 1.0

4. Wind forces shall be applied in the directions resulting in maximum member forces and reactions. For towers with square cross-sections,
wind forces shall be multiplied by the following factor when the wind is directed along a tower diagonal:

1 + 0. 75e, but not > 1.2

5. Wind forces on tower appurtenances such as ladders, conduits, lights, elevators, etc., shall be calculated using appropriate force
coefficients for these elements.

6. Notation:

e\ ratio of solid area to gross area of one tower face for the segment under consideration.

Figure 207D.5-2

Other Structures Force Coefficients, Cf Trussed Towers of All Heights

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-130 CHAPTER 2 - Minimum Design Loads

207E Wind Loads - Components and Cladding
(C&C)

Commentary:

In developing the set of pressure coefficients applicable for
the design of components and cladding (C&C) as given in
Figures 207 E. 4- 1, 207E.4-2A, 207E.4-2B, 207E.4-2C,
207E.4-3, 207E.4-4, 207E.4-5A, 207E.4-5B, and 207E.4-
6 , an envelope approach was followed but using different
methods than for the MWFRS of Figure 2 07 C. 4-1. Because
of the small effective area that may be involved in the
design of a particular component (consider, e.g. , the
effective area associated with the design of a fastener), the
point wise pressure fluctuations may be highly correlated
over the effective area of interest. Consider the local purlin
loads shown in Figure C207C4-L The approach involved
spatial averaging and time averaging of the point
pressures over the effective area transmitting loads to the
purlin while the building model was permitted to rotate in
the wind tunnel through 360°. As the induced localized
pressures may also vary widely as a function of the specific
location on the building, height above ground level,
exposure, and more importantly, local geometric
discontinuities and location of the element relative to the
boundaries in the building surfaces (walls, roof lines),
these factors were also enveloped in the wind tunnel tests.
Thus, for the pressure coefficients given in Figures 207E.4-
1, 207E.4-2A, 207E.4-2B, 207E.4-2C, 207EA-3, 207E.4-4,
207E.4-5A, 207E.4-5B, and 207E.4-6, the directionality of
the wind and influence of exposure have been removed and
the surfaces of the building "zoned” to reflect an envelope
of the peak pressures possible for a given design
application.

As indicated in the discussion for Figure 207C.4-1, the
wind tunnel experiments checked both Exposure B and C
terrains. Basically ( GC p ) values associated with Exposure
B terrain would be higher than those for Exposure C
terrain because of reduced velocity pressure in Exposure
B terrain. The ( GC p ) values given in Figures 207E.4-1,
207E.4-2A, 207E.4-2B, 207E.4-2C , 207E.4-3, 207E.4-4,
207E.4-5A, 207E.4-5B, and 207E.4-6 are associated with
Exposure C terrain as obtained in the wind tunnel.
However, they may also be used for any exposure when the
correct velocity pressure representing the appropriate
exposure is used as discussed below.

The wind tunnel studies conducted by ESDU (1990)
determined that when low-rise buildings (h < 18 m) are
embedded in suburban terrain (Exposure B), the pressures
on components and cladding in most cases are lower than
those currently used in the standards and codes, although
the values show a very large scatter because of high
turbulence and many variables. The results seem to

indicate that some reduction in pressures for components
and cladding of buildings located in Exposure B i s
justified. Hence, the code permits the use of the applicable
exposure category when using these coefficients.

The pressure coefficients given in Figure 207 E. 6- 1 for
buildings with mean height greater than 18 m were
developed following a similar approach, but the influence
of exposure was not enveloped (Stathopoulos and
Dumitrescu-Brulotte 1989). Therefore, exposure

categories B, C, or D may be used with the values of (GCf)
in Figure 207E.6-I as appropriate.

207E.1 Scope

207E.1.1 Building Types

This chapter applies to the determination of wind pressures
on components and cladding (C&C) on buildings.

1. Part 1 is applicable to an enclosed or partially
enclosed:

• Low-rise building (see definition in

Section 207A.2)

• Building with h < 18 m

The building has a flat roof, gable roof, multispan
gable roof, hip roof, monoslope roof, stepped roof, or
sawtooth roof and the wind pressures are calculated
from a wind pressure equation.

2. Part 2 is a simplified approach and is applicable to an
enclosed:

• Low-rise building (see definition in

Section 207A.2)

• Building with h < 18 m

The building has a flat roof, gable roof, or hip roof and
the wind pressures are determined directly from a
table.

3. Part 3 is applicable to an enclosed or partially
enclosed:

• Building with h > 18 m

The building has a flat roof, pitched roof, gable roof,
hip roof, mansard roof, arched roof, or domed roof and
the wind pressures are calculated from a wind pressure
equation.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-131

4. Part 4 is a simplified approach and is applicable to an
enclosed:

• Building with h < 48 m

The building has a flat roof, gable roof, hip roof,
monoslope roof, or mansard roof and the wind
pressures are determined directly from a table.

5. Part 5 is applicable to an open building of all heights
having a pitched free roof, monoslope free roof, or
trough free roof.

6. Part 6 is applicable to building appurtenances such as
roof overhangs and parapets and rooftop equipment.

207E.1.2 Conditions

A building whose design wind loads are determined in
accordance with this chapter shall comply with all of the
following conditions:

1 . The building is a regular-shaped building as defined in
Section 207A.2.

2. The building does not have response characteristics
making it subject to across wind loading, vortex
shedding, or instability due to galloping or flutter; or it
does not have a site location for which channeling
effects or buffeting in the wake of upwind obstructions
warrant special consideration.

207E1.3 Limitations

The provisions of this chapter take into consideration the
load magnification effect caused by gusts in resonance with
along-wind vibrations of flexible buildings. The loads on
buildings not meeting the requirements of Section
207E.1.2, or having unusual shapes or response
characteristics, shall be determined using recognized
literature documenting such wind load effects or shall use
the wind tunnel procedure specified in Section 207F.

207E.1.4 Shielding

There shall be no reductions in velocity pressure due to
apparent shielding afforded by buildings and other
structures or terrain features.

207E.1.5 Air-Permeable Cladding

Design wind loads determined from Section 207E shall be
used for air-permeable cladding unless approved test data
or recognized literature demonstrates lower loads for the
type of air-permeable cladding being considered.

Commentary:

Air-permeable roof or wall claddings allow partial air
pressure equalization between their exterior and interior
surfaces. Examples include siding, pressure-equalized rain
screen walls, shingles, tiles , concrete roof pavers, and
aggregate roof surfacing .

The peak pressure acting across an air-permeable
cladding material is dependent on the characteristics of
other components or layers of a building envelope
assembly . At any given instant the total net pressure across
a building envelope assembly will be equal to the sum of
the partial pressures across the individual layers as shown
in Figure C207E.1-1. However, the proportion of the total
net pressure borne by each layer will vary from instant to
instant due to fluctuations in the external and internal
pressures and will depend on the porosity and stiffness of
each layer , as well as the volumes of the airspaces between
the layers . As a result, although there is load sharing
among the various layers, the sum of the peak pressures
across the individual layers will typically exceed the peak
pressure across the entire system. In the absence of
detailed information on the division of loads, a simple,
conservative approach is to assign the entire differential
pressure to each layer designed to carry load.

To maximize pressure equalization (reduction) across any
cladding system (irrespective of the permeability of the
cladding itself), the layer or layers behind the cladding
should be:

• relatively stiff in comparison to the cladding material
and

• relatively air-impermeable in comparison to the
cladding material.

Furthermore, the air space between the cladding and the
next adjacent building envelope surface behind the
cladding (e.g., the exterior sheathing) should be as small
as practicable and compartmentalized to avoid
communication or venting between different pressure
zones of a building 's surfaces.

The design wind pressures derived from Section 207 E
represent the pressure differential between the exterior and
interior surfaces of the exterior envelope (wall or roof
system). Because of partial air-pressure equalization
provided by air-permeable claddings, the components and
cladding pressures derived from Section 207E can
overestimate the load on air-permeable cladding elements .
The designer may elect either to use the loads derived from
Section 207 E or to use loads derived by an approved
alternative method. If the designer desires to determine the

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-132 CHAPTER 2 - Minimum Design Loads

pressure differential across a specific cladding element in
combination with other elements comprising a specific
building envelope assembly, appropriate full-scale
pressure measurements should be made on the applicable
building envelope assembly, or reference should be made
to recognized literature (Cheung and Melbourne 1986 ,
Haig 1990, Baskaran 1992, Southern Building Code
Congress International 1994, Peterka et ai 1997, ASTM
2006, 2007, and Kala et ai 2008) for documentation
pertaining to wind loads. Such alternative methods may
vary according to a given cladding product or class of
cladding products or assemblies because each has unique
features that affect pressure equalization.

EXTERIOR LAVERySH EATING
V WALL CAVITY

CLADDING

INTERIOR LAYER/FINISH

BUILDING

EXTERIOR

BUILDING

INTERIOR

B-R = pressure differential across cladding layer
fjj-? = pressure dfferential across exterior layer/sheathing
B-q = pressure dfferential across interior layer/finish

Figure C207E.1-1

Distribution of Net Components and Cladding Pressure Acting on a Building Surface
(Building Envelope) Comprised of Three Components (Layers)

207E.2 General Requirements

207E.2.1 Wind Load Parameters Specified in Section
207A

The following wind load parameters are specified in
Section 207A:

Basic Wind Speed V (Section 207A.5)

Wind directionality factor K d (Section 207A.6)
Exposure category (Section 207A.7)
Topographic factor K zt (Section 207A.8)

Gust Effect Factor (Section 207A.9)

Enclosure classification (Section 207 A. 10)

Association of Structural Engineers of the Philippines, Inc, (ASEP)

CHAPTER 2 - Minimum Design Loads 2-1 33

• Internal pressure coefficient ( GC pi )

(Section 207A.11).

207E.2.2 Minimum Design Wind Pressures

The design wind pressure for components and cladding of
buildings shall not be less than a net pressure of 0.77 kN/m 2
acting in either direction normal to the surface.

207E.2.3 Tributary Areas Greater than 65 m 2

Component and cladding elements with tributary areas
greater than 65 m 2 shall be permitted to be designed using
the provisions for MWFRS.

207E.2.4 External Pressure Coefficients

Combined gust effect factor and external pressure
coefficients for components and cladding, (GC p ), are
given in the figures associated with this chapter. The
pressure coefficient values and gust effect factor shall not
be separated.

207E.3 Velocity Pressure

207E.3.1 Velocity Pressure Exposure Coefficient

Based on the exposure category determined in
Section 207A.7.3, a velocity pressure exposure coefficient
K z or K h , as applicable, shall be determined from
Table 207E.3-1. For a site located in a transition zone
between exposure categories, that is, near to a change in
ground surface roughness, intermediate values of K z or
K h , between those shown in Table 207E.3-1, are permitted,
provided that they are determined by a rational analysis
method defined in the recognized literature.

Commentary:

See commentary, Section C207B.3.L

207E.3.2 Velocity Pressure

Velocity pressure, q z , evaluated at height z shall be
calculated by the following equation:

q z = 0. 613 K z K zt K d V 2 (N/m 2 );V in
m/s

(207E.3-1)

where

K zt = topographic factor defined, see
Section 207A.8

V = basic wind speed, see Section 207A.5
q h = velocity pressure calculated using
Equation 207E.3-1 at height h

The numerical coefficient 0.613 shall be used except where
sufficient climatic data are available to justify the selection
of a different value of this factor for a design application.

Commentary:

See commentary, Section C207B.3.2.

Figures 207E.4-1, 207E.4-2A, 207E.4-2B, and

207E.4-2C. The pressure coefficient values provided in
these figures are to be used for buildings with a mean roof
height of 18 m or less . The values were obtained from wind-
tunnel tests conducted at the University of Western Ontario
(Davenport et al 1977, 1978), at the James Cook
University of North Queensland (Best and Holmes 1978),
and at Concordia University (Stathopoulos 1981,
Stathopoulos and Zhu 1988, Stathopoulos and Luchian
1990, 1992, and Stathopoulos and Saathoff 1991). These
coefficients were refined to reflect results of full-scale tests
conducted by the National Bureau of Standards (Marshall
1977) and the Building Research Station, England (Eaton
and Moyne 1975). Pressure coefficients for hemispherical
domes on the ground or on cylindrical structures were
based on wind-tunnel tests (Taylor 1991). Some of the
characteristics of the values in the figure are as follows:

1. The values are combined values of ( GC p ). The gust
effect factors from these values should not be
separated.

2. The velocity pressure q h evaluated at mean roof
height should be used with all values of (GC V ).

3. The values provided in the figure represent the upper
bounds of the most severe values for any wind
direction. The reduced probability that the design
wind speed may not occur in the particular direction
for which the worst pressure coefficient is recorded
has not been included in the values shown in the
figure.

4. The wind-tunnel values, as measured, were based on
the mean hourly wind speed. The values provided in
the figures are the measured values divided by (1.53) 2
(see Figure C207A.5-1) to adjust for the reduced
pressure coefficient values associated with a 3-s gust
speed.

= wind directionality factor, see Section
207A.6

= velocity pressure exposure coefficient, see
Section 207E.3.1

National Structural Code of the Philippines Volume I, 7th Edition, 2015

Each component and cladding element should be designed
for the maximum positive and negative pressures
(including applicable internal pressures) acting on it. The

2-134 CHAPTER 2 - Minimum Design Loads

pressure coefficient values should be determined for each
component and cladding element on the basis of its
location on the building and the effective area for the
element. Research (Stathopoulos and Zhu 1988 , 1990)
indicated that the pressure coefficients provided generally
apply to facades with architectural features , such as
balconies , ribs , and various facade textures . In ASCE 7-02,
the roof slope range and values of (GC p ) were updated
based on subsequent studies (Stathopoulos et al. 1999,
2000 , 2001 ).

Figures 207E.4-4 , 207E.4-5A, and 207E.4-5B. These
figures present values of (GC p ) for the design of roof
components and cladding for buildings with multispan
gable roofs and buildings with monoslope roofs. The
coefficients are based on wind tunnel studies (Stathopoulos
and Mohammadian 1986, Suny and Stathopoulos 1988,
and Stathopoulos and Saathoff 1991).

Figure 207E.4-6. The values of ( GC p ) in this figure are for
the design of roof components and cladding for buildings
with sawtooth roofs and mean roof height, h, less than or
equal to 18 m. Note that the coefficients for corner zones
on segment A differ from those coefficients for corner zones
on the segments designated as B, C, and D . Also, when the
roof angle is less than or equal to 10°, values of ( GC p )for
regular gable roofs (Figure 207E.4-2A) are to be used. The
coefficients included in Figure 207E.4-6 are based on wind
tunnel studies reported by Saathoff and Stathopoulos
(1992).

Figure 207E.4- 7. This figure for cladding pressures on
dome roofs is based on Taylor (1991). Negative pressures
are to be applied to the entire surface, because they apply
along the full arc that is perpendicular to the wind
direction and that passes through the top of the dome.
Users are cautioned that only three shapes were available
to define values in this figure (h D /D — 0 . 5 , f/D =
0 . 5 ; h D /D = 0 . 0 , f/D = 0 . 5 ; and h D /D = 0 . 0 , //
D = 0 . 33 ).

Figure 207E.6-1. The pressure coefficients shown in this
figure reflect the results obtained from comprehensive
wind tunnel studies carried out (Stathopoulos and
Dumitrescu-Brulotte 1989). The availability of more
comprehensive wind tunnel data has also allowed a
simplification of the zoning for pressure coefficients, flat
roofs are now divided into three zones, and walls are
represented by two zones.

The external pressure coefficients and zones given in
Figure 207E.6-1 were established by wind tunnel tests on
isolated " box-like " buildings (Akins and Cermak 1975 and
Peterka and Cermak 1975). Boundary-layer wind-tunnel
tests on high-rise buildings (mostly in downtown city
centers) show that variations in pressure coefficients and
the distribution of pressure on the different building
facades are obtained (Templin and Cermak 1978). These
variations are due to building geometry, low attached
buildings, nonrectangular cross-sections, setbacks, and
sloping surfaces. In addition, surrounding buildings
contribute to the variations in pressure. Wind tunnel tests
indicate that pressure coefficients are not distributed
symmetrically and can give rise to torsional wind loading
on the building.

Boundary-layer wind-tunnel tests that include modeling of
surrounding buildings permit the establishment of more
exact magnitudes and distributions of (GCp) for buildings
that are not isolated or <( boxlike ” in shape.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

Table 207E.3-1

Velocity Pressure Exposure Coefficients, K h and K z

Height above ground level, z

Exposure

(m)

0-4.5

0.70

0.85

1.03

6.0

0.70

0.90

1.08

7.5

0.70

0.94

1.12

9.0

0.70

0.98

1.16

12.0

0.76

1.04

1.22

15.0

0.81

1.09

1.27

18.0

0.85

1.13

1.31

21.0

0.89

1.17

1.34

24.0

0.93

1.21

1.38

27.0

0.96

1.24

1.40

30.0

0.99

1.26

1.43

36.0

1.04

1.31

1.48

42.0

1.09

1.36

1.52

48.0

1.13

1.39

1.55

54.0

1.17

1.43

1.58

60.0

1.20

1.46

1.61

75.0

1.28

1.53

1.68

90.0

1.35

1.59

1.73

105.0

1.41

1.64

1.78

120.0

1.47

1.69

1.82

135.0

1.52

1.73

1.86

150.0

1.56

1.77

1.89

Notes:

1 . The velocity pressure exposure coefficient K z may be determined from the following formula:

For 4.57 m < z < z g For z< 4.57 m

K z = 2 . 01 (z/z g ) 2/ “ K z = 2. 01(4. 57 /z g ) 2/ “

2. a and z g are tabulated in Table 207A.9-1 .

3. Linear interpolation for intermediate values of height z is acceptable.

4. Exposure categories are defined in Section 207A.7.

2-135

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-136 CHAPTER 2 - Minimum Design Loads

Part 1: Low-Rise Buildings

207E.4.2 Design Wind Pressures

Commentary:

The component and cladding tables in Figure 207E.5-1 are
a tabulation of the pressures on an enclosed \ regular , 9-m
high building with a roof as described. The pressures can
be modified to a different exposure and height with the
same adjustment factors as the MWFRS pressures . For the
designer to use this method for the design of the
components and cladding, the building must conform to all
five requirements in Section 207 E. 6 ; otherwise one of the
other procedures specified in Section 207E.1.1 must be
used.

207E.4 Building Types

The provisions of Section 207E.4 are applicable to an
enclosed and partially enclosed:

• Low-rise building (see definition in Section 207A.2)

• Building with h < 1 8 m

The building has a flat roof, gable roof, multispan gable
roof, hip roof, monoslope roof, stepped roof, or sawtooth
roof. The steps required for the determination of wind loads
on components and cladding for these building types are
shown in Table 207E.4-1.

207E.4.1 Conditions

For the determination of the design wind pressures on the
components and claddings using the provisions of
Section 207E.4.2 the conditions indicated on the selected
figure(s) shall be applicable to the building under
consideration.

Design wind pressures on component and cladding
elements of low-rise buildings and buildings with
h < 18 m shall be determined from the following equation:

V = qfc[(CCp) - (GC pi )] (N/m 2 ) 207E.4-1

where

q z = velocity pressure evaluated at mean roof
height h as defined in Section 207E.3
(GC p ) = external pressure coefficients given in:

• Figure 207E.4-1 (walls)

• Figures. 207E.4-2A to 207E.4-2C (flat
roofs, gable roofs, and hip roofs)

• Figure 207E.4-3 (stepped roofs)

• Figure 207E.4-4 (multispan gable roofs)

• Figures 207E.4-5A and 207E.4-5B
(monoslope roofs)

• Figure 207E.4-6 (sawtooth roofs)

• Figure 207E.4-7 (domed roofs)

• Figure 207B.4-3, footnote 4 (arched roofs)

(GC A = internal pressure coefficient given in
Pl Table 207 A. 11-1

User Note;

Use Part 1 of Section 207 E to determine wind pressures
on C&C of enclosed and partially enclosed low-rise
buildings having roof shapes as specified in the
applicable figures. The provisions in Part 1 are based
on the Envelope Procedure with wind pressures
calculated using the specified equation as applicable to
each building surface. For buildings for which these
provisions are applicable this method generally yields
the lowest wind pressures of all analytical methods
contained in this code.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-137

Table 207E.4-1

Steps to Determine C&C Wind Loads
Enclosed and Partially Enclosed
Low-rise Buildings

Step 1 : Determine risk category of building or other
structure, see Table 103-1

Step 2: Determine the basic wind speed, V, for the
applicable risk category, see Figure 207A.5-
1A, BorC

Step 3: Determine wind load parameters:

> Wind directionality factor, K d , see
Section 207A.6 and Table 207A.6-1

> Exposure category B, C or D, see Section
207A.7

> Topographic factor, K zt , see Section
207 A.8 and Figure 207A.8-1

> Enclosure classification, see Section
207 A. 10

> Internal pressure coefficient, (GC pi ), see
Section 207A.1 1 and Table 207A.1 1-1

Step 4:

Determine

velocity

pressure

exposure

coefficient

K z or K h ,

see Table 207E.3-1

Step 5:

Determine velocity
Equation 207E.3-1

pressure,

q h , see

Step 6:

Determine

(GC P )

external

pressure

coefficient,

> Walls, see Figure 207E.4-1

> Flat roofs, gable roofs, hip roofs, see
Figure 207E.4-2

> Stepped roofs, see Figure 207E.4-3

> Multispan gable roofs, see Figure 207E.4-
4

> Monoslope roofs, see Figure 207E.4-5

> Sawtooth roofs, see Figure 207E.4-6

> Domed roofs, see Figure 207E.4-7

> Arched roofs, see Figure 207B.4-3
footnote 4

Step 7 : Calculate wind pressure, p, Equation 207E.4- 1

Part 2: Low-Rise Buildings (Simplified)

207E.5 Building Types

The provisions of Section 207E.5 are applicable to an
enclosed:

• Low-rise building (see definition in Section 207A.2)

• Building with h < 18 m

The building has a flat roof, gable roof, or hip roof The
steps required for the determination of wind loads on
components and cladding for these building types are
shown in Table 207E.5- 1 .

207E.5.1 Conditions

For the design of components and cladding the building
shall comply with all the following conditions:

1 . The mean roof height h must be less than or equal to
18 m (i.e. h < 18 m).

2. The building is enclosed as defined in
Section 207A.2 and conforms to the wind-borne debris
provisions of Section 207A.10.3.

3. The building is a regular-shaped building or structure
as defined in Section 207A.2.

4. The building does not have response characteristics
making it -subject to across wind loading, vortex
shedding, or instability due to galloping or flutter; and
it does not have a site location for which channeling
effects or buffeting in the wake of upwind obstructions
warrant special consideration.

5. The building has either a flat roof, a gable roof with
9 < 45°, or a hip roof with 0 < 27°.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-138 CHAPTER 2 - Minimum Design Loads

207E.5.2 Design Wind Pressures

Net design wind pressures, p nef , for component and
cladding of buildings designed using the procedure
specified herein represent the net pressures (sum of internal
and external) that shall be applied normal to each building
surface as shown in Figure 207E.5-1. p net shall be
determined by the following equation:

Pnet = AK zt Pnet9 (207E.5-1)

where

A adjustment factor for building height and

exposure from Figure 207E.5-1
K zt = topographic factor as defined in
Section 207A.8 evaluated at 0.33 mean
roof height, 0. 33Ji

Pnet30 = net design wind pressure for Exposure B,
at h = 9 m, from Figure 207E.5-1

User Note :

Part 2 of Section 207E is a simplified method to
determine wind pressures on C&C of enclosed low-rise
buildings having flat , gable or hip roof shapes . The
provisions of Part 2 are based on the Envelope
Procedure of Part 1 with wind pressures determined
from a table and adjusted as appropriate.

Table 207E.5-1
Steps to Determine C&C
Wind Loads Enclosed Low-rise Buildings
(Simplified Method)

Step Determine risk category, see Table 103-1
1 :

Step Determine the basic wind speed, V , for the

2: applicable risk category, see Figure 207A.5-

1A, B or C

Step Determine wind load parameters:

> Exposure category B, C or D, see Section
207A.7

> Topographic factor, K zt , see Section
207A.8 and Figure 207A.8-1

Step Enter figure to determine wind pressures

4: at h = 9 m., p net9? see Figure 207E.5-1

Step Enter figure to determine adjustment for

5: building height and exposure, A, see Figure

207E.5-1

Step Determine adjusted wind pressures, p net , see

6: Equation 207E.5-1.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-139

Part 3: Buildings with ft > 18 m

207E.6.2 Design Wind Pressures

Commentary :

In Equation 207E.6-1 a velocity pressure term , qi, appears
that is defined as the “velocity pressure for internal
pressure determination. ’* The positive internal pressure is
dictated by the positive exterior pressure on the windward
face at the point where there is an opening. The positive
exterior pressure at the opening is governed by the value
of q at the level of the opening, not q h . For positive internal
pressure evaluation , q t may conservatively be evaluated at
height ft (q t = q h ). For low buildings this does not make
much difference , but for the example of a 91.5-m-tall
building in Exposure B with the highest opening at 18 m,
the difference between q 915 and q 1Q represents a 59
percent increase in internal pressure . This is unrealistic
and represents an unnecessary degree of conservatism.
Accordingly , q t = q z for positive internal pressure
evaluation in partially enclosed buildings where height z
is defined as the level of the highest opening in the building
that could affect the positive internal pressure. For
buildings sited in wind-borne debris regions , glazing that
is not impact resistant or protected with an impact
protective system, q t should be treated as an opening.

207E.6 Building Types

The provisions of Section 207E.6 are applicable to an
enclosed or partially enclosed building with a mean roof
height ft > 18 m with a flat roof, pitched roof, gable roof,
hip roof, mansard roof, arched roof, or domed roof. The
steps required for the determination of wind loads on
components and cladding for these building types are
shown in Table 207E.6-1.

207E.6.1 Conditions

For the determination of the design wind pressures on the
component and cladding using the provisions of
Section 207E.6.2, the conditions indicated on the selected
flgure(s) shall be applicable to the building under
consideration.

Design wind pressures on component and cladding for all
buildings with ft> 18 m shall be determined from the
following equation:

p = q{GC p ) - (GC pi ) (N/m 2 ) 207E.6-1

where

(GC P )

(GCpi)

q z for windward walls calculated at height z
above the ground

q h for leeward walls, side walls, and roofs
evaluated at height ft

q h for windward walls, side walls, leeward
walls, and roofs of enclosed buildings and for
negative internal pressure evaluation in
partially enclosed buildings
q z for positive internal pressure evaluation in
partially enclosed buildings where height z is
defined as the level of the highest opening in
the building that could affect the positive
internal pressure. For positive internal
pressure evaluation, q t may conservatively be
evaluated at height h(qi = qh)

External pressure coefficients given in:

• Figure 207E.6-1 for walls and flat roofs

• Figure 2 07 B. 4- 3, footnote 4, for arched
roofs

• Figure 207E.4-7 for domed roofs

• Note 6 of Figure 207E.6- 1

Internal pressure coefficient given in
Table 207A.11-1

q and q t shall be evaluated using exposure defined in
Section 207A.1 1-1

Exception;

In buildings with a mean roof height ft greater than 18 m
and less than 27.4 m, (GC P ) values from Figures 207E.4-
1 through 207E.4-6 shall be permitted to be used if the
height to width ratio is one or less.

User Note :

Section Part 3 of Section 207 E for determining wind
pressures for C&C of enclosed and partially enclosed
buildings with h > 18 m having roof shapes as specified
in the applicable figures. These provisions are based on
the Directional Procedure with wind pressures
calculated from the specified equation applicable to
each building surface.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-140 CHAPTER 2 - Minimum Design Loads

Table 207E.6-1

Steps to Determine C&C Wind Loads
Enclosed and Partially Enclosed
Building with h > 18 m

Step 1;

Determine risk category, see Table 103-1

Step 2:

Determine the basic wind speed, V, for the
applicable risk category, see Figure 207A.5-
1A, B or C

Step 3 :

Determine wind load parameters:

Wind directionality factor, K& see
Section 207A.6 and Table 207 A. 6-1

Exposure category B, C or D, see Section
207A.7

Topographic factor, K zt , see Section
207A.8 and Figure 207A.8-1

Enclosure classification, see Section
207A.10

Internal pressure coefficient, ( GC pi ), see
Section 207 A. 11 and Table 207A.11-1

Step 4:

Determine velocity pressure exposure
coefficient K z or K see Table 207E.3-1

Step 5:

Determine velocity pressure, q h , see Table
207E.3-1

Step 6:

Determine external pressure coefficient,

(GC P )

Walls and flat roofs, (0 < 10°), see
Figure 207E.6-1

Gable and hip roofs, see Figure 207E.4-2
per Note 6 of Figure 207E.6-1

Arched roofs, see Figure 207B.4-3,
footnote 4

Domed roofs, see Figure 207E.4-7

Step 7;

Calculate wind pressure, p, Equation 207E.6-
1

Part 4: Buildings with h < 48 m (Simplified)

Commentary :

This section has been added to ASCE 7-10 to cover the
common practical case of enclosed buildings up to height
h=49m. Table 207E. 7-2 includes wall and roof pressures
for fat roofs (0 < 10°), gable roofs, hip roofs, monoslope
roofs, and mansard roofs. Pressures are derived from
Figure 207E.6-1 (flat roofs), Figure 207 E. 4-2 A. B. and C
(gable and hip roofs), and Figure 207 E. 4-5 A and B
(monos lope roofs) of Part 3. Pressures were selected for
each zone that encompasses the largest pressure
coefficients for the comparable zones from the different
roof shapes. Thus, for some cases, the pressures tabulated
are conservative in order to maintain simplicity. The ( GC p )
values from these figures were combined with an infernal
pressure coefficient (+ or 0. 1 8) to obtain a net coefficient
from which pressures were calculated. The tabulated
pressures are applicable to the entire zone shown in the
various figures.

Pressures are shown for an effective wind area of 0.93 m 2 .
A reduction factor is also shown to obtain pressures for
larger effective wind areas. The reduction factors are
based on the graph of external pressure coefficients shown
in the figures in Part 3 and are based on the most
conservative reduction for each zone from the various
figures.

207E.7 Building Types

The provisions of Section 207E.7 are applicable to an
enclosed building having a mean roof height h < 49 m
with a flat roof, gable roof, hip roof, monoslope roof, or
mansard roof. The steps required for the determination of
wind loads on components and cladding for these building
types are shown in Table 207E.7-1.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 Minimum Design Loads

2-141

207E.7.1 Wind Loads — Components and Cladding

207E.7.1.1 Wail and Roof Surfaces

Design wind pressures on the designated zones of wails
and roofs surfaces shall be determined from
Table 207E.7-2 based on the applicable basic wind speed
V , mean roof height h , and roof slope 6. Tabulated
pressures shall be multiplied by the exposure adjustment
factor (EAF) shown in the table if exposure is different
than Exposure C. Pressures in Table 207E.7-2 are based on
an effective wind area of 0.93 m 2 . Reductions in wind
pressure for larger effective wind areas may be taken based
on the reduction multipliers (RF) shown in the table.
Pressures are to be applied over the entire zone shown in
the figures. Final design wind pressure shall be determined
from the following equation:

V = Ptabie(EAF)(RF)K zt (207E.7-1)

where

RF ~ effective area reduction factor from

Table 207E.7-2

EAF = Exposure adjustment factor from
Table 207E.7-2

K zt = topographic factor as defined in

Section 207A.8

207E.7.1.2 Parapets

Design wind pressures on parapet surfaces shall be based
on wind pressures for the applicable edge and corner zones
in which the parapet is located, as shown in
Table 207E.7-2, modified based on the following two load
cases:

• Load Case A shall consist of applying the applicable
positive wall pressure from the table to the front
surface of the parapet while applying the applicable
negative edge or corner zone roof pressure from the
table to the back surface.

• Load Case B shall consist of applying the applicable
positive wall pressure from the table to the back of the
parapet surface and applying the applicable negative
wall pressure from the table to the front surface.

User Note.

Part 4 of Section 207 E is a simplified method for
determining wind pressures for C&C of enclosed and
partially enclosed buildings with h <49 m. having roof
shapes as specified in the applicable figures. These
provisions are based on the Directional Procedure from
Part 3 with wind pressures selected directly from a table
and adjusted as applicable.

Table 207E.7-1

Steps to Determine C&C Wind Loads
Enclosed Building with h > 48.8 ?n

Step Determine risk category, see Table 103-1
1:

Step Determine the basic wind speed, V , for the

2: applicable risk category, see Figure 207A.5-

1A, BorC

Step Determine wind load parameters:

> Exposure category B, C or D, see Section
207A.7

Step Enter Table 207E.7-2 to determine pressure on
4: walls and roof, p, using Equation 207E.7-1.

Roof types are:

> Flat roof (0 < 10 °)

> Gable roof

> Hip roof

^ Monoslope roof

> Mansard roof

Step Determine topographic factors, K zt , and apply
5: factor to pressures determined from tables (if

applicable), see Section 207A.8

Pressures in Table 207E.7-2 are based on an effective wind
area of 0.93 m 2 . Reduction in wind pressure for larger
effective wind area may be taken based on the reduction
factor shown in the table. Pressures are to be applied to the
parapet in accordance with Figure 207E.7-1. The height h
to be used with Figure 207E.7-1 to determine the pressures
shall be the height to the top of the parapet. Determine final
pressure from Equation 207E.7-1.

Commentary :

Parapet component and cladding wind pressures can be
obtained from the tables as shown in the parapet figures

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-142 CHAPTER 2 - Minimum Design Loads

from the table. The pressures obtained are slightly
conservative based on the net pressure coefficients for
parapets compared to roof zones from Part 3. Two load
cases must be considered based on pressures applied to
both windward and leeward parapet surfaces as shown in
Figure 207E.7-1.

207E.7.1.3 Roof Overhangs

Design wind pressures on roof overhangs shall be based on
wind pressures shown for the applicable zones in Table
207E.7-2 modified as described herein. For Zones 1 and 2,
a multiplier of 1.0 shall be used on pressures shown in
Table 207E.7-2. For Zone 3, a multiplier of 1.15 shall be
used on pressures shown in Table 207E.7-2.

Pressures in Table 207E.7-2 are based on an effective wind
area of 0.93 m 2 . Reductions in wind pressure for larger
effective wind areas may be taken based on the reduction
multiplier shown in Table 207E.7-2. Pressures on roof
overhangs include the pressure from the top and bottom
surface of overhang. Pressures on the underside of the
overhangs are equal to the adjacent wall pressures. Refer to
the overhang drawing shown in Figure 207E.7-2.
Determine final pressure from Equation 207E.7-1.

Commentary:

Component and cladding pressures for roof overhangs can
be obtained from the tables as shown in Figure 207E. 7-2.
These pressures are slightly conservative and are based on
the external pressure coefficients contained in Figure
207E.4-2A to 207E.4-2C from Part 3.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-143

Monoslope Roof

Mansard Roof

Flat Roof

0 < 1 0 deg

l 1

Gable Roof

Figure 207E.7-2

C & C Zones C&C Wall and Roof Pressures, h < 48 m
Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-144

CHAPTER 2 - Minimum Design Loads

Roof and Wall Pressures-Components and Cladding
Exposure Adjustment Factor

Notes to Component and Cladding Wind Pressure Table:

1. For each roof form, Exposure C, V and h determine roof and wall cladding pressures for the applicable zone from tables
above. For other exposures B or D, multiply pressures from table by the appropriate exposure adjustment factor determined
from figure above.

2. Interpolation between h values is permitted. For pressures at other V values than shown in the table, multiply table value
for any given V 'in the table as shown above:

Pressure at desired V = pressure from table at V ’x[V desired/^ ] 2

3. Where two load cases are shown, both positive and negative pressures shall be considered.

4. Pressures are shown for an effective wind area = 0.93 m 2 . For larger effective wind areas, the pressure shown may be
reduced by the reduction coefficient applicable to each zone.

Notation:

h mean roof height (m)

V Basic wind speed (kph)

Table 207E.7-2 (continued)

C & C Zones C&C Wall and Roof Pressures, h < 48 m
Enclosed Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-145

Reduction Factors
Effective Wind Area

Roof Form

Sign Pressure

Zone 1

Zone 2

Zone 3

Zone 4

Zone 5

Flat

Minus

Flat

Plus

Gable, Mansard

Minus

Gable, Mansard

Plus

Hip

Minus

Hip

Plus

Monoslope

Minus

Monoslope

Plus

Overhangs

All

Table 207E.7-2 (continued)

C & C Effective Wind Area C&C Wall and Roof Pressures, h < 48 m
Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-146 CHAPTER 2 - Minimum Design Loads

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 150 -200 kph, ft = 4.5 - 15 m
Exposure C

V (kph)

150

200

h (m)

Roof Form

Load

Case

Zone

Flat Roof

[

-1.5579

-2.4453

-3.3328

-1.0649

1.0649

-1.9523

1.0649

-2.7696

-4.3473

-5.9249

-1.8932

1.8932

-3.4708

1.8932

Gable Roof
Mansard Roof

-1.1635

0.6705

-1.9523

0.6705

-2.9384

0.6705

-1.2621

1.1635

-1.9523

1 .0649

-2.0685

1.1920

-3.4708

1.1920

-5.2238

1.1920

-2.2438

2.0685

-3.4708

1.8932

Hip Roof

-1.0649

0.6705

-1.8537

0.6705

-2.7412

0.6705

-1.2621

1.1635

-1.9523

1 .0649

*1.8932

1.1920

-3.2955

1.1920

-4.8732

1.1920

-2.2438

2.0685

-3.4708

1.8932

Monoslope

Roof

-1.3607

0.5719

-1.7551

0.5719

-3.0370

0.5719

-1.2621

1.1635

-1.9523

1 .0649

-2.4191

1.0167

-3.1202

1.0167

-5.3990

1.0167

-2.2438

2.0685

-3.4708

1.8932

Flat Roof

-1.4865

-2.3332

-3.1799

-1.0161

1.0161

-1.8628

1.0161

-2.6426

-4.1479

-5.6531

-1.8063

1.8063

-3.3116

1.8063

Gable Roof
Mansard Roof

-1.1101

0.6397

-1.8628

0.6397

-2.8036

0.6397

-1.2042

1.1101

-1.8628

1.0161

-1.9736

1.1373

-3.3116

1.1373

-4.9841

1.1373

-2.1408

1.9736

-3.3116

1.8063

Hip Roof

-1.0161

0.6397

-1.7687

0.6397

-2.6154

0.6397

-1.2042

1.1101

-1.8628

1.0161

■1.8063

1.1373

-3.1444

1.1373

-4.6496

1.1373

-2.1408

1.9736

-3.3116

1.8063

Monoslope

Roof

-1.2983

0.5457

-1.6746

0.5457

-2.8977

0.5457

-1.2042

1.1101

-1.8628

1.0161

-2.3081

0.9701

-2.9771

0.9701

-5.1514

0.9701

-2.1408

1.9736

-3.3116

1.8063

Flat Roof

-1.4007

-2.1986

-2.9964

-0.9574

0.9574

-1.7553

0.9574

-2.4901

-3.9086

-5.3270

-1.7021

1.7021

-3.1206

1.7021

Gable Roof
Mansard Roof

-1.0461

0.6028

-1.7553

0.6028

-2.6418

0.6028

-1.1347

1.0461

-1.7553

0.9574

-1.8597

1.0717

-3.1206

1.0717

-4.6966

1.0717

-2.0173

1.8597

-3.1206

1.7021

Hip Roof

-0.9574

0.6028

-1.6667

0.6028

-2.4645

0.6028

-1.1347

1.0461

-1.7553

0.9574

*1.7021

1.0717

-2.9629

1.0717

-4.3814

1.0717

-2.0173

1.8597

-3.1206

1.7021

Monoslope

Roof

-1.2234

0.5142

-1.5780

0.5142

-2.7305

0.5142

-1.1347

1.0461

-1.7553

0.9574

-2.1749

0.9141

-2.8053

0.9141

-4.8542

0.9141

-2.0173

1.8597

-3.1206

1.7021

7.5

Flat Roof

-1.3435

-2.1088

-2.8741

-0.9184

0.9184

-1.6837

0.9184

-2.3885

-3.7490

-5.1096

-1.6326

1.6326

-2.9932

1.6326

Gable Roof
Mansard Roof

-1.0034

0.5782

-1.6837

0.5782

-2.5340

0.5782

-1.0884

1.0034

-1.6837

0.9184

-1.7838

1.0280

-2.9932

1.0280

-4.5049

1.0280

-1.9350

1.7838

-2.9932

1.6326

Hip Roof

-0.9184

0.5782

-1.5986

0.5782

-2.3639

0.5782

-1.0884

1.0034

-1.6837

0.9184

-1.6326

1 .0280

-2.8420

1.0280

-4.2025

1.0280

-1.9350

1.7838

-2.9932

1.6326

Monoslope

Roof

-1.1735

0.4932

-1.5136

0.4932

-2.6190

0.4932

-1.0884

1.0034

-1.6837

0.9184

-2.0862

0.8768

-2.6908

0.8768

-4.6561

0.8768

-1.9350

1.7838

-2.9932

1.6326

Flat Roof

-1.2864

-2.0191

-2.7518

-0.8793

0.8793

-1.6120

0.8793

-2.2869

-3.5895

-4.8921

-1.5632

1.5632

-2.8658

1.5632

Gable Roof
Mansard Roof

-2.8658

0.9842

-4.3132

0.9842

-1.8526

1.7079

-2.8658

1.5632

Hip Roof

-0.8793

0.5536

-1.5306

0.5536

-2.2633

0.5536

-1.0421

0.9607

-1.6120

0.8793

-1.5632

0.9842

-2.7211

0.9842

-4.0237

0.9842

-1.8526

1.7079

-2.8658

1.5632

Monoslope

Roof

-1.1235

0.4722

-1.4492

0.4722

-2.5076

0.4722

-1.0421

0.9607

-1.6120

0.8793

-1.9974

0.8395

-2.5763

0.8395

-4.4579

0.8395

-1.8526

1.7079

-2.8658

1.5632

4.5

Flat Roof

-1.2149

-1.9069

-2.5990

-0.8304

0.8304

-1.5225

0.8304

-2.1598

-3.3901

-4.6204

-1.4763

1.4763

-2.7066

1.4763

Gable Roof
Mansard Roof

-0.9073

0.5229

-1.5225

0.5229

-2.2914

0.5229

-0.9842

0.9073

-1.5225

0.8304

-1.6130

0.9295

-2.7066

0.9295

-4.0736

0.9295

-1.7497

1.6130

-2.7066

1.4763

Hip Roof

-0.8304

0.5229

-1.4456

0.5229

-2.1376

0.5229

-0.9842

0.9073

-1.5225

0.8304

-1.4763

0.9295

-2.5699

0.9295

-3.8002

0.9295

-1.7497

1.6130

-2.7066

1.4763

Monoslope

Roof

-1.0611

0.4460

-1.3687

0.4460

-2.3683

0.4460

-0.9842

0.9073

-1.5225

0.8304

-1.8864

0.7928

-2.4332

0.7928

-4.2103

0.7928

-1.7497

1.6130

-2.7066

1.4763

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-147

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 250 -300 kph, ft = 4.5 - 15 m
Exposure C

V (kph)

250

300

h(m)

Roof Form

Load

Zone

Case

Flat Roof

-4.3276

-6.7926

-9.2577

-2.9581

-5.4232

-6.2317

-9.7814

-13.3311

-4.2596

-7.8093

2.9581

4.2596

Gable Roof

-3.2320

-5.4232

-8.1621

-3.5059

-5.4232

-4.6541

-7.8093

-11.7534

-5.0485

-7.8093

1 ^

Mansard Roof

1.8625

3.2320

2.9581

2.6820

4.6541

4.2596

Hip Roof

-2.9581

-5.1493

-7.6143

-3.5059

-5.4232

-4.2596

-7.4149

-10.9646

-5.0485

-7.8093

1.8625

3.2320

2.9581

2.6820

4.6541

4.2596

Monoslope

-3.7798

-4.8754

-8.4360

-3.5059

-5.4232

-5.4429

-7.0205

-12.1479

-5.0485

-7.8093

Roof

1.5886

3.2320

2.9581

2.2876

4.6541

4.2596

Flat Roof

-4.1291

-6.4810

-8.8330

-2.8224

-5.1744

-5.9458

-9.3327

-12.7196

-4.0642

-7.4511

2.8224

4.0642

Gable Roof

-3.0837

-5.1744

-7.7877

-3.3451

-5.1744

-4.4406

-7.4511

-11.2143

-4.8169

-7.4511

1 7

Mansard Roof

1.7771

3.0837

2.8224

2.5590

4.4406

4.0642

Hip Roof

-2.8224

-4.9131

-7.2650

-3.3451

-5.1744

-4.0642

-7.0748

-10.4617

-4.8169

-7.4511

1.7771

3.0837

2.8224

2.5590

4.4406

4.0642

Monoslope

-3.6064

-4.6517

-8.0490

-3.3451

-5.1744

-5.1932

-6.6985

-11.5906

-4.8169

-7.4511

Roof

1.5157

3.0837

2,8224

2.1826

4.4406

4.0642

Flat Roof

-3.8908

-6.1071

-8.3234

-2.6596

-4.8759

-5.6028

-8.7943

-11.9858

-3.8298

-7.0212

2.6596

3.8298

Gable Roof

-2.9058

-4.8759

-7.3384

-3.1521

-4.8759

-4.1844

-7.0212

-10.5673

-4.5390

-7.0212

Mansard Roof

1.6745

2.9058

2.6596

2.4113

4.1844

3.8298

Hip Roof

-2.6596

-4.6296

-6.8459

-3.1521

-4.8759

-3.8298

-6.6666

-9.8581

-4.5390

-7.0212

1.6745

2.9058

2.6596 '

2.4113

4.1844

3.8298

Monoslope

-3.3983

-4.3834

-7.5847

-3.1521

-4.8759

-4.8936

-6.3120

-10.9219

-4.5390

-7.0212

Roof

1.4283

1 .4283

1.4283

2.9058

2.6596

2.0567

4.1844

3.8298

Flat Roof

-3.7320

-5.8579

-7.9837

-2.5510

-4.6768

-5.3741

-8.4353

-11.4965

-3.6735

-6.7347

2.5510

3.6735

Gable Roof

-2.7872

-4.6768

-7.0389

-3.0234

-4.6768

-4.0136

-6.7347

-10,1360

-4.3537

-6.7347

7.5

Mansard Roof

1.6062

1.6062 |

1.6062

2.7872

2.5510

2.3129

2*3129

2.3129

4.0136

3.6735

Hip Roof

-2.5510

-4.4406

-6.5665

-3.0234

-4.6768

-3.6735

-6.3945

-9.4557

-4.3537

-6.7347

1.6062

1 .6062

1.6062

2.7872

2.5510

2.3129

4.0136

3.6735

Monoslope

-3.2596

-4.2044

-7.2751

-3.0234

-4.6768

-4.6939

-6.0544

-10.4761

-4.3537

-6.7347

Roof

1.3700

2.7872

2.5510

1.9728

4.0136

3.6735

Flat Roof

-3.5732

-5.6086

-7.6440 j

-2.4425

-4.4778

-5.1454

-8.0764

-11.0073

-3.5171

-6.4481

2.4425

3.5171

Gable Roof

-2.6686

-4.4778

-6.7394

-2.8948

-4.4778

-3.8428

-6.4481

-9.7047

-4.1685

-6.4481

Mansard Roof

1.5378

2.6686

2.4425

2.2145

3.8428

3.5171

Hip Roof

-2.4425

-4.2517

-6.2871

-2.8948

-4.4778

-3.5171

-6.1224

-9.0534

-4.1685

-6.4481

1.5378

2.6686

2.4425

2.2145

3.8428

3.5171

Monoslope

-3.1209

-4.0255

-6.9655

-2.8948

-4.4778

-4.4941

-5.7968

-10.0303

-4.1685

-6.4481

Roof

1.3117

2.6686

2.4425

1.8888

3.8428

3.5171

Flat Roof

-3.3747

-5.2970

-7.2193

-2.3068

-4.2291

-4.8596

-7.6277

-10.3958

-3.3217

-6.0899

2.3068

3.3217

Gable Roof

-2.5204

-4.2291

-6.3650

-2.7339

-4.2291

-3.6293

-6.0899

-9.1655

-3.9369

-6.0899

4.5

Mansard Roof

1.4524

2.5204

2.3068

2.0915

3.6293

3.3217

Hip Roof

-2.3068

-4.0155

-5.9378

-2.7339

-4.2291

-3.3217

-5.7823

-8.5504

-3.9369

-6.0899

1.4524

2.5204

2.3068

2.0915

3.6293

3.3217

Monoslope

-2.9475

-3.8019

-6.5785

-2.7339

-4.2291

-4.2444

-5.4747

-9.4731

-3.9369

-6.0899

Roof

1.2388

2.5204

2.3068

1.7839

3.6293

3.3217

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-148 CHAPTER 2 - Minimum Design Loads

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 350 kph, h = 4.5 - 15 m
Exposure C

V (kph)

350

/i(m)

Roof Form

Load

Zone

Case

-8.4820

-13.3136

-18.1451

-5.7978

-10.6294

Flat Roof

5.7978

Gable Roof

-6.3347

-10.6294

-15.9978

-6.8715

-10.6294

Mansard Roof

3.6505

6.3347

5.7978

-5.7978

-10.0925

-14,9241

-6.8715

-10.6294

Hip Roof

3.6505

6.3347

5.7978

Monoslope

-7.4084

-9.5557

-16.5346

-6.8715

-10.6294

Roof

3.1137

6.3347

5.7978

-8.0929

-12.7029

-17.3128

-5.5319

-10.1418

Flat Roof

5.5319

5.5319 1

Gable Roof

-6.0441

-10.1418

-15.2639

-6.5563

-10.1418

Mansard Roof

3.4830

6.0441

5.5319

-5.5319

-9.6296

-14.2395

-6.5563

-10.1418

Hip Roof

3.4830

6.0441

5.5319

Monoslope

-7.0685

-9.1174

-15.7761

-6.5563

-10.1418

Roof

2.9708

6.0441

5.5319

-7.6260

-11.9700

-16.3139

-5.2127

-9.5567

Flat Roof

5.2127

Gable Roof

-5.6954

-9.5567

-14.3833

-6.1781

-9.5567

Mansard Roof

3.2821

5.6954

5.2127

-5.2127

-9.0740

-13.4180

-6.1781

-9.5567

Hip Roof

3.2821

5.6954

5.2127

Monoslope

-6.6607

-8.5914

-14.8660

-6.1781

-9.5567

Roof

2.7994

5.6954

5.2127

-7.3148

-11,4814

-15.6481

-5.0000

-9.1666

Flat Roof

5.0000

Gable Roof

-5.4629

-9.1666

-13.7962

-5.9259

-9.1666

Mansard Roof

3.1481

5.4629

5.0000

7.5

-5.0000

-8.7037

-12.8703

-5.9259

-9.1666

Hip Roof

3.1481

5.4629

5.0000

Monoslope

-6.3889

-8.2407

-14.2592

-5.9259

-9.1666

Roof

2.6852

5.4629

5.0000

-7.0035

-10.9929

-14.9822

-4.7872

-8.7766

Flat Roof

4.7872

Gable Roof

-5.2305

-8.7766

-13.2092

-5.6737

-8.7766

Mansard Roof

3.0142

5.2305

4.7872

-4.7872

-8.3333

-12.3226

-5.6737

! -8.7766

Hip Roof

3.0142

5.2305

4.7872

Monoslope

-6.1170

-7.8900

-13.6524

-5.6737

-8.7766

Roof

2.5709

5.2305

4.7872

-6.6144

-10.3821

-14.1498

-4.5213

-8.2890

Flat Roof

4.5213

Gable Roof

-4.9399

-8.2890

-12.4753

-5.3585

-8.2890

Mansard Roof

2.8467

4.9399

4.5213

4.5

-4.5213

-7.8703

-11.6380

-5.3585

-8.2890

Hip Roof

2.8467

4.9399

4.5213

Monoslope

-5.7772

-7.4517

-12.8939

-5.3585

-8.2890

Roof

2.4281

| 2.4281

' 4.9399

4.5213

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-149

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 1 50 -200 kph, h = 1 8 - 33 m
Exposure C

V (kph)

150

200

h(m)

Roof Form

Load

Case

Zone

Flat Roof

-1.8438

-2.8940

-3.9443

-1.2603

1.2603

-2.3106

1.2603

-3.2778

-5.1450

-7.0121

-2.2405

2.2405

-4.1077

2.2405

Gable Roof
Mansard Roof

-1.3770

0.7935

-2.3106

0.7935

-3.4775

0.7935

-1.4937

1.3770

-2.3106

1.2603

-2.4480

1.4107

-4.1077

1.4107

-6.1822

1.4107

-2.6555

2.4480

-4.1077

2.2405

Hip Roof

-1.2603

0.7935

-2.1939

0.7935

-3.2441

0.7935

-1.4937

1.3770

-2.3106

1.2603

-2.2405

1.4107

-3.9002

1.4107

-5.7673

1.4107

-2.6555

2.4480

-4.1077

2.2405

Monoslope

Roof

-1.6104

0.6768

-2.0772

0.6768

-3.5942

0.6768

-1.4937

1.3770

-2.3106

1.2603

-2.8629

1 .2033

-3.6927

1.2033

-6.3897

1.2033

-2.6555

2.4480

-4.1077

2.2405

Flat Roof

-1.8009

-2.8267

-3.8526

-1.2310

1.2310

-2.2568

1.2310

-3.2016

-5.0253

-6.8490

-2.1884

2.1884

-4.0121

2.1884

Gable Roof
Mansard Roof

-1.3450

0.7751

-2.2568

0.7751

-3.3966

0.7751

-1.4590

1.3450

-2.2568

1.2310

-2.3911

1.3779

-4.0121

1.3779

-6.0385

1.3779

-2.5937

2.3911

-4.0121

2.1884

Hip Roof

-1.2310

0.7751

-2.1428

0.7751

-3.1687

0.7751

-1.4590

1.3450

-2.2568

1.2310

-2.1884

1.3779

-3.8095

1.3779

-5.6332

1.3779

-2.5937

2.3911

-4.0121

2.1884

Monoslope

Roof

-1.5729

0.6611

-2.0289

0.6611

-3.5106

0,6611

-1.4590

1.3450

-2.2568

1.2310

-2.7963

1.1753

-3.6069

1.1753

-6.2411

1.1753

-2.5937

2.3911

-4.0121

2.1884

Flat Roof

-1.7723

-2.7819

-3.7914

-1.2115

1.2115

-2.2210

1.2115

-3.1508

-4.9455

-6.7403

-2.1537

2.1537

-3.9485

2.1537

Gable Roof
Mansard Roof

-1.3236

0.7628

-2.2210

0.7628

-3.3427

0.7628

-1.4358

1.3236

-2.2210

1.2115

-2.3531

1.3560

-3.9485

1.3560

-5.9426

1.3560

-2.5525

2.3531

-3.9485
2.1537 |

Hip Roof

-1

-1.2115

0.7628

-2.1088

0.7628

-3.1184

0.7628

-1.4358

1.3236

-2.2210

1.2115

-2.1537

1.3560

-3.7490

1.3560

-5.5438

1.3560

-2.5525

2.3531

-3.9485

2.1537

Monoslope

Roof

-1.5480

0.6506

-1.9967

0.6506

-3.4549

0.6506

-1.4358

1.3236

-2.2210

1.2115

-2.7520

1.1566

-3,5496

1.1566

-6.1420

1.1566

-2.5525

2.3531

-3.9485

2.1537

Flat Roof

-1.7294

-2.7146

-3.6997

-1.1821

1.1821

-2.1673

1.1821

-3.0746

-4.8259

-6.5772

-2.1016

2.1016

-3.8529

2.1016

Gable Roof
Mansard Roof

-1.2916

0.7443

-2.1673

0.7443

-3.2619

0.7443

-1.4011

1.2916

-2.1673

1.1821

-2.2962

1.3232

-3.8529

f.3232

-5.7988

1.3232

-2.4908

2.2962

-3.8529

2.1016

Hip Roof

-1.1821

0.7443

-2.0578

0.7443

-3.0429

0.7443

-1.4011

1.2916

-2.1673

1.1821

-2.1016

1.3232

-3.6583

1.3232

-5.4097

1.3232

-2.4908

2.2962

-3.8529

2.1016

Monoslope

Roof

-1.5105

0.6349

-1.9484

0.6349

-3.3713

0.6349

-1.4011

1.2916

-2.1673

1.1821

-2.6854

1.1286

-3.4637

1.1286

-5.9934

1.1286

-2.4908

2.2962

-3.8529

2.1016

Flat Roof

-1.6723

-2.6248

-3.5774

-1.1431

1.1431

-2.0956

1.1431

-2.9729

-4.6664

-6.3598

-2.0321

2.0321

-3.7256

2.0321

Gable Roof
Mansard Roof

-1.2489

0.7197

-2.0956

0.7197

-3.1540

0.7197

-1.3547

1.2489

-2.0956

1.1431

-2.2203

1.2795

-3.7256

1.2795

-5.6072

1.2795

■2.4084

2.2203

-3.7256

2.0321

Hip Roof

-1.1431

0.7197

-1.9898

0.7197

-2.9423

0.7197

-1.3547

1.2489

-2.0956

1.1431

-2.0321

1.2795

-3.5374

1.2795

-5.2308

1.2795

-2.4084

2.2203

-3.7256

2.0321

Monoslope

Roof

-1.4606

0.6139

-1.8839

0,6139

-3.2599

0.6139

-1.3547

1.2489

-2.0956

1.1431

-2.5966

1.0913

-3.3492

1.0913

-5.7953

1.0913

-2.4084

2.2203

-3.7256

2.0321

Flat Roof

-1.6151

-2.5351

-3.4551

-1,1040

1.1040

-2.0240

1.1040

-2.8713

-4.5068

-6.1424

-1.9626

1.9626

-3.5982

1.9626

Gable Roof
Mansard Roof

-1.2062

0.6951

-2.0240

0.6951

-3.0462

0.6951

-1.3084

1.2062

-2.0240

1.1040

-2.1444

1.2357

-3.5982

1.2357

-5.4155

1.2357

-2.3261

2.1444

-3.5982

1.9626

Hip Roof

-1.1040

0.6951

-1.9218

0.6951

-2.8417

0.6951

-1.3084

1.2062

-2.0240

1.1040

-1.9626

1.2357

-3.4165

1.2357

-5.0520

1.2357

-2.3261

2.1444

-3.5982

1.9626

Monoslope

Roof

-1.4107

0.5929

-1.8195
0.5929 ,

-3.1484

0.5929

-1.3084

1.2062

-2.0240

1.1040

-2.5078

1.0540

-3.2347

1.0540

-5.5972

1 .0540

-2.3261

2.1444

-3.5982

1.9626

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-150 CHAPTER 2 - Minimum Design Loads

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 250 -300 kph, h = 18 - 33 m
Exposure C

V (kph)

250

300

Load

Zone

h (m)

Roof Form

Case

-5.1216

-8.0390

-10.9564

-3.5009

-6.4182

-7.3751

-11.5761

-15.7772

-5.0412

-9.2422

Flat Roof

3.5009

5.0412

Gable Roof

-3.8250

-6.4182

-9.6598

-4.1492

-6.4182

-5.5080

-9.2422

-13.9100

-5.9748

-9.2422

Mansard Roof

2.2042

3.8250

3.5009

3.1741

5.5080

5.0412

-3.5009

-6.0941

-9.0114

-4.1492 1

-6.4182

-5.0412

-8.7755

-12.9765

-5.9748

-9.2422

Hip Roof

2.2042

3.8250

3.5009

3.1741

5.5080

5.0412

Monoslope

-4.4733

-5.7699

-9.9839

-4.1492

-6.4182

-6.4416 1

-8.3087

-14.3768

-5.9748

-9.2422 |

Roof

1.8801

3.8250

3.5009

2.7073

5.5080

5.0412

-5.0025

-7.8520

-10.7016

-3.4194

-6.2690

-7.2036

-11,3069

-15.4103

-4.9240

-9.0273

Flat Roof

3.4194 1

3.4194

4.9240

Gable Roof

-3.7360

-6.2690

-9.4351

-4.0527

-6.2690

-5.3799

-9.0273

-13.5866

-5.8358

-9.0273

Mansard Roof

2.1530

2.1530 1

3.7360

3.4194

3.1003

5.3799

4.9240

-3.4194

-5.9524

-8.8019

-4.0527

-6.2690

-4.9240

-8.5714

-12.6747

-5.8358

-9.0273

Hip Roof

2.1530

3.7360

3.4194

3.1003

5.3799

4.9240 1

Monoslope

-4.3693

-5.6357

-9.7517

-4.0527

-6.2690

-6.2918

-8.1155

-14.0425

-5.8358

-9.0273

Roof

1.8364

3.7360

3.4194

2.6444

5.3799

4.9240

-4.9231

-7.7274

-10.5317

-3.3652

-6.1695

-7.0893

-11.1275

-15.1656

-4.8458

-8.8840

Flat Roof

3.3652

4.8458

Gable Roof

-3.6767

-6.1695

-9.2853

-3.9883

-6.1695

-5.2945

-8.8840

13.3709

-5.7432

-8.8840 1

Mansard Roof

2.1188

3.6767

3.3652

3.0511

5.2945

4.8458

-3.3652

-5.8579

-8.6622

-3.9883

-6.1695

-4.8458

-8.4353

-12.4735

-5.7432

-8.8840

Hip Roof

2.1188

3.6767

3.3652

3.0511

5.2945

4.8458

Monoslope

-4.2999

-5.5463

-9.5969

-3.9883

-6.1695

-6.1919

-7.9866

-13.8196

-5.7432

-8.8840

Roof

1.8072

3.6767

3.3652

2.6024

5.2945

4.8458

-4.8040

-7.5404

-10.2769

-3.2837

-6.0202

-6.9178

-10.8582

-14.7987

-4.7286

-8.6691

Flat Roof

3.2837

4.7286

Gable Roof

-3.5878

-6.0202

-9.0607

-3.8918

-6.0202

-5.1664

-8.6691

-13.0474

-5.6043

-8.6691

Mansard Roof

2.0675

3.5878

3.2837

2.9773

5.1664

4.7286

-3.2837

-5.7161

-8.4526

-3.8918

-6.0202

-4.7286

-8.2313

-12.1717

-5.6043

-8.6691

Hip Roof

2.0675

3.5878

3.2837

2.9773

5.1664

4.7286

Monoslope

-4.1959

-5.4121

-9.3647

-3.8918

-6.0202

-6.0421

-7.7934

-13.4852

-5.6043

-8.6691

Roof

1.7635

1,7635

1.7635

3.5878

3.2837

2.5394

5.1664

4.7286

-4.6452

-7.2912

-9.9372

-3.1752

-5.8212

-6.6891

-10.4993

-14.3095

-4.5723

-8.3825

Flat Roof

3.1752

4.5723

4,5723

Gable Roof

-3.4692

-5.8212

-8.7612

-3.7632

-5.8212

-4.9956

-8.3825

-12.6161

-5.4190

-8.3825

Mansard Roof

1.9992

3.4692

3.1752

2.8788

4.9956

4.5723

-3.1752

-5.5272

-8.1732

-3.7632

-5.8212

-4.5723

-7.9591

-11.7694

-5.4190

-8.3825

Hip Roof

1.9992

3.4692

3.1752

2.8788

4.9956

4.5723

Monoslope

-4.0572

-5.2332

-9.0552

-3.7632

-5.8212

-5.8423

-7.5358

-13.0394

-5.4190

-8.3825

Roof

1.7052

3.4692

3.1752

2.4555

4.9956

4.5723

-4.4864

-7.0419

-9.5974

-3.0666

-5.6222

-6.4604

-10.1403

-13.8203

-4.4160

-8.0959

Flat Roof

3.0666

4.4160

Gable Roof

-3.3506

-5.6222

-8.4616

-3.6345

-5.6222

-4.8248

-8.0959

-12.1848

-5.2337

-8.0959

Mansard Roof

1.9308

1,9308

1.9308

3.3506

3.0666

2.7804

4.8248

4.4160

-3.0666

-5.3382

-7.8937

-3.6345

-5.6222

-4.4160

-7.6870

-11.3670

-5.2337

-8.0959

Hip Roof

1.9308

3.3506

3.0666

2.7804

4.8248

4.4160

Monoslope

-3.9185

-5.0543

-8.7456

-3.6345

-5.6222

-5.6426

-7.2782

-12.5937

-5.2337

-8.0959

Roof

| 1.6469

1.6469

[ 3.3506

3.0666

2.3715

4.8248

4.4 160

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 350 kph, h = 1 8 - 33 m
Exposure C

V (kph)

350

h (m)

Roof Form

Load

Zone

Case

Flat Roof

-10.0384

-15.7564

-21.4745

-6.8617

-12.5797

6.8617

Gable Roof

-7.4970

-12.5797

18.9331

-8.1323

-12.5797

Mansard Roof

4.3203

7.4970

6.8617

Hip Roof

-6.8617

-11.9444

-17.6624

-8.1323

-12.5797

4.3203

7.4970

6.8617

Monoslope

-8.7677

-11.3090

-19.5685

-8.1323

-12.5797 1

Roof

3.6850

7.4970

6.8617

Flat Roof

-9.8049

-15.3900

-20.9751

-6.7021

-12.2872

6.7021

Gable Roof

-7.3227

-12.2872

-18.4928

-7.9432

-12.2872

Mansard Roof

4.2198

7.3227

6.7021

Hip Roof

-6.7021

-11.6666

-17.2517

-7.9432

-12.2872

4.2198

7.3227

6.7021

Monoslope

-8.5638

-11.0460

-19.1134

-7.9432

-12.2872

Roof

3.5993

7.3227

6.7021

Flat Roof

-9.6493

-15.1457

-20.6421

-6.5957

-12.0921

6.5957

Gable Roof

-7.2064

-12.0921

-18.1993

-7.8171

-12.0921

Mansard Roof

4.1529

4,1529

7.2064

6.5957

Hip Roof

-6.5957

-11.4814

-16.9778

-7.8171

-12.0921

4.1529

4,1529

4.1529

7.2064

6.5957

Monoslope

-8.4279

-10.8707

-18.8100

-7.8171

-12.0921

Roof

3.5421

7.2064

6.5957

Flat Roof

-9.4158

-14.7793

-20.1427

-6.4361

-11.7996 1

6.4361

Gable Roof

-7.0321

-11.7996

-17.7590

-7.6280

-11.7996

Mansard Roof

4.0524

7.0321

6.4361

Hip Roof

-6.4361

-11.2036

-16.5671

-7.6280

-11.7996

4.0524

7.0321

6.4361

Monoslope

| -8.2240

-10.6077

-18.3549

-7.6280

-11.7996

Roof

3.4564

7.0321

6.4361

Flat Roof

-9.1046

-14.2907

-19.4768

-6.2234

-11.4095

6.2234

Gable Roof

-6.7996

-11.4095

-17.1719

-7.3758

-11.4095

Mansard Roof

3.9184

6.7996

6.2234

Hip Roof

-6.2234

-10.8333

-16.0194

-7.3758

-11.4095

3.9184

6.7996

6.2234

Monoslope

-7.9521

-10.2570

-17.7481

-7.3758

-11,4095

Roof

3,3422

3.3422

6.7996

6.2234

Flat Roof

-8.7933

-13.8021

-18.8110

-6,0106

*11.0194

6.0106

Gable Roof

-6.5671

-11.0194

-16.5848

-7.1237

-11.0194

Mansard Roof

3.7845

6.5671

6.0106 |

Hip Roof

-6.0106

-10.4629

-15.4717

-7.1237

-11.0194

3.7845

6.5671

6.0106

Monoslope

-7.6802

-9.9064

-17.1414

-7.1237

-11.0194

Roof

3.2279

6.5671

6.0106

2-151

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-152 CHAPTER 2 - Minimum Design Loads

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 150 -200 kph, h = 36 - 48 m
Exposure C

V (kph)

150

200

h(m)

Roof Form

Load

Case

Zone

Flat Roof

-1.9867

-3.1184

-4.2501

-1.3580

1.3580

-2.4897

1.3580

-3.5319

-5.5438

-7.5556

-2.4142

2.4142

-4.4261

2.4142

Gable Roof
Mansard Roof

-1.4837

0.8550

-2.4897

0.8550

-3.7471

0.8550

-1.6095

1.4837

-2.4897

1.3580

-2.6378

1.5201

-4.4261

1.5201

-6.6615

1.5201

-2.8613

2.6378

-4.4261

2.4142

Hip Roof

-1.3580

0.8550

-2.3639

0.8550

-3.4956

0.8550

-1.6095

1.4837

-2.4897

1.3580

-2.4142

1.5201

-4.2025

1.5201

-6.2144

1.5201

-2.8613

2.6378

-4.4261

2.4142

Monoslope

Roof

-1.7352

0.7293

-2.2382

0.7293

-3.8728

0.7293

-1.6095

1.4837

-2.4897

1.3580

-3.0848

1.2965

-3.9790

1.2965

-6.8850

1.2965

-2.8613

2.6378

-4.4261

2.4142

Flat Roof

■1.9724

-3.0959

-4.2195

-1.3482

1.3482

-2.4718

1.3482

-3.5065

-5.5039

-7.5013

-2.3969

2.3969

-4.3942

2.3969

Gable Roof
Mansard Roof

-1.4731

0.8489

-2.4718

0.8489

-3.7201

0.8489

-1.5979 !

1.4731

-2.4718

1.3482

-2.6188

1.5091

-4.3942

1.5091

-6.6136

1.5091

-2.8407

2.6188

-4.3942

2.3969

Hip Roof

-1.3482

0.8489

-2.3469

0.8489

-3.4705

0.8489

-1.5979

1.4731

-2.4718

1.3482

-2.3969

1.5091

-4.1723

1.5091

-6.1697

1.5091

-2.8407

2.6188

-4.3942

2.3969

Monoslope

Roof

-1.7227

0.7241

-2.2221

0.7241

-3.8450

0.7241

-1.5979

1.4731

-2.4718

1.3482

-3.0627

1.2872

-3.9504

1.2872

-6.8355

1.2872

-2.8407

2.6188 '

-4.3942

2.3969

Flat Roof

-1.9438

: na

-3.0511

-4.1583

-1.3287

1.3287

-2.4359

1.3287

-3.4557

-5.4241

-7.3926

-2.3621

2.3621

-4.3306

2.3621

Gable Roof
Mansard Roof

-2.4359

0.8366

-3.6662

0.8366

-1.5747

1.4517

-2.4359

1.3287

-2.5808

1.4873

-4.3306

1 .4873

-6.5177

1.4873

-2.7996

2.5808

-4.3306

2.3621

Hip Roof

-2.3129

0.8366

-1.5747

1.4517

-2.4359

1.3287

-2.3621

1.4873

-4.1118

1.4873

-6.0803

1,4873

-2.7996

2.5808

-4.3306

2.3621

Monoslope

Roof

H88

-2.1899

0.7136

-3.7892

0.7136

-1.5747

1.4517

-2.4359

1.3287

-3.0183

1.2685

-3.8931

1.2685

-6.7364

1.2685

-2.7996

2.5808

-4.3306

2.3621

Flat Roof

-1,9152

-3.0062

-4.0972

-1.3092

1.3092

-2.4001

1.3092

-3.4049

-5.3444

-7.2839

-2.3274

2.3274

-4.2669

2.3274

Gable Roof
Mansard Roof

-1.4304

0.8243

-2.4001

0.8243

-3.6123

0.8243

-1.5516

1.4304

-2.4001

1.3092

-2.5429

1 .4654

-4.2669

1.4654

-6.4219

1.4654

-2.7584

2.5429

-4.2669

2.3274

Hip Roof

-1.3092

0.8243

-2.2789

0.8243

-3.3699

0,8243

-1.5516

1.4304

-2.4001

1.3092

-2.3274

1.4654

-4.0514

1.4654

-5.9909

1.4654

-2.7584

2.5429

-4.2669

2.3274

Monoslope

Roof

-1.6728

0.7031

-2.1577

0.7031

-3.7335

0.7031

-1.5516

1.4304

-2.4001

1.3092

-2.9739

1.2499

-3.8359

1.2499

-6.6374

1.2499

-2.7584

2.5429

-4.2669

2.3274

Flat Roof

-1.8724

-2.9389

-4.0054

-1.2798

1.2798

-2.3464

1.2798

-3.3287

-5.2247

-7.1208

-2.2753

2.2753

-4.1713

2.2753

Gable Roof
Mansard Roof

-1.3984

0.8058

-2.3464

0.8058

-3.5314

0.8058

-1.5169

1.3984

-2.3464

1.2798

-2.4860

1 .4326

-4.1713

1.4326

-6.2781

1.4326

-2.6966

2.4860

-4.1713

2.2753

Hip Roof

-1.2798

0.8058

-2.2279

0.8058

-3.2944

0.8058

-1.5169

1.3984

-2.3464

1.2798

-2.2753

1.4326

-3.9607

1.4326

-5.8567

1.4326

-2.6966

2.4860

-4.1713

2.2753

Monoslope

Roof

-1.6354

0.6873

-2.1094

0.6873

-3.6499

0.6873

-1.5169

1.3984

-2.3464

1.2798

‘2.9073

1.2219

-3.7500

1.2219

-6.4888

1.2219

-2.6966

2.4860

-4.1713

2,2753

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-153

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 250 -300 kph, h = 36 - 48 m
Exposure C

V (kph)

250

300

h (m)

Roof Form

Load

Zone

Case

Flat Roof

-5.5 1 86

-8.6622

-11.8057

-3.7722

-6.9158

-7.9468

-12.4735

■17.0002

-5.4320

-9.9587

3.7722

5 4320

5.4320

Gable Roof

-4.1215

-6.9158

-10.4086

-4.4708

-6.9158

-5.9350

-9.9587

-14.9883

-6.4379

-9.9587

Mansard Roof

2.3751

4.1215

3.7722

3.4202

5.9350

5.4320

Hip Roof

-3.7722

-6.5665

-9.7100

-4.4708

-6.9158

-5.4320

-9.4557

-13.9824

-6.4379

-9.9587

2.3751

4.1215

3.7722

3.4202

5.9350

5.4320

Monoslope

-4.8201

-6.2172

-10.7579

-4.4708

-6.9158

-6.9409

-8.9528

-15.4913

-6.4379

-9.9587

Roof

2.0258

4.1215

3.7722

2.9172

5.9350

5.4320

Flat Roof

-5.4789

-8.5998

-11.7208

-3.7451

-6.8660

-7.8897

-12.3838

-16.8779

-5.3929

-9.8871

3.7451

5.3929

Gable Roof

-4.0919

-6.8660

-10.3337

-4.4386

-6.8660

-5.8923

-9.8871

-14.8805

-6.3916

-9.8871

Mansard Roof

2.3580

4.0919

3.7451

3.3956

5.8923

5.3929

Hip Roof

-3.7451

-6.5192

-9.6402

-4.4386

-6.8660

-5.3929

-9.3877

-13.8818

-6.3916

-9.8871

2.3580

4.0919

3.7451

3.3956

5.8923

5.3929

Monoslope

-4.7854

-6.1725

-10.6805

-4.4386

-6.8660

-6.8910

-8.8884

-15.3799

-6.3916

-9.8871

Roof

2.0113

4.0919

3.7451

2.8962

5.8923

5.3929

Flat Roof

-5.3995

-8.4752

-11.5509

-3.6908

-6.7665

-7.7753

-12.2043

-16.6333

-5.3148

-9.7438

3.6908

5.3148

Gable Roof

-4.0326

-6.7665

-10.1839

-4.3743

-6.7665

-5.8069

-9.7438

-14.6649

-6.2990

-9.7438

Mansard Roof

2.3238

4.0326

3.6908

3.3463

5.8069

5.3148

Hip Roof

-3.6908

-6.4248

-9.5004

-4.3743

-6.7665

-5.3148

-9.2517

-13.6806

-6.2990

-9.7438

2.3238

4.0326

3.6908

3.3463

5.8069

5.3148

Monoslope

-4.7160

-6.0830

-10.5257

-4.3743

-6.7665

-6.7911

-8.7595

-15.1570

-6.2990

-9.7438

Roof

1.9821

4.0326

3.6908

2.8542

5.8069

5.3148

Flat Roof

-5.3201

-8.3506

-11.3810

-3.6365

-6.6670

-7.6610

-12.0248

-16.3887

-5.2366

-9.6005

3.6365

5.2366

Gable Roof

-3.9733

-6.6670

-10.0342

-4.3100

-6.6670

-5.7215

-9.6005

-14.4492

-6.2064

-9.6005

Mansard Roof

2.2897

3.9733

3.6365

3.2971

5.7215

5.2366

Hip Roof

-3.6365

-6.3303

-9.3607

-4.3100

-6.6670

-5.2366

-9.1156

-13.4794

-6.2064

-9.6005

2.2897

3.9733

3.6365

3.2971

5.7215

5.2366

Monoslope

-4.6467

-5.9936

-10.3709

-4.3100

-6.6670

-6.6912

-8.6307

-14.9341

-6.2064

-9.6005

Roof

1.9530

3.9733

3.6365

2.8123

5.7215

5.2366

Flat Roof

-5.2010

-8.1636

-11.1262

-3.5551

-6.5177

-7.4895

-11.7556

-16.0218

-5.1194

-9.3855

3.5551

5.1194

Gable Roof

-3.8843

-6.5177

-9.8095

-4.2135

-6.5177

-5.5934

-9.3855

-14.1257

-6.0674

-9.3855

Mansard Roof

2.2384

3.8843

3.5551

3.2233

5.5934

5.1194

Hip Roof

-3.5551

-6.1886

-9.1512

-4.2135

-6.5177

-5.1194

-8.9115

-13.1777

-6.0674

-9.3855

2.2384

3.8843

3.5551

3.2233

5.5934

5.1194

Monoslope

-4.5427

-5.8594

-10.1387

-4.2135

-6.5177

-6.5414

-8.4375

-14.5997

-6.0674

-9,3855

Roof

1.9092

3.8843

3.5551

2.7493

5.5934

5.1194

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-154 CHAPTER 2 - Minimum Design Loads

Table 207E.7-2

Components and Cladding - Part 4
C&C, V = 350 kph, h = 36 - 48 m
Exposure C

V (kph)

350

h(m)

Roof Form

Load

Case

Zone

Flat Roof

-10.8165

-16.9778

-23.1392

-7.3936

7.3936

-13.5549

7.3936

Gable Roof
Mansard Roof

-8.0782

4.6552

-13.5549

4.6552

-20.4008

4.6552

-8.7628

8.0782

-13.5549

7.3936

Hip Roof

-7.3936

4.6552

-12.8703

4.6552

-19.0316

4.6552

-8.7628

8.0782

-13.5549

7.3936

Monoslope Roof

-9.4474

3.9706

-12.1857

3.9706

-21.0854

3.9706

-8.7628

8.0782

-13.5549

7.3936

Flat Roof

-10.7387

-16.8557

-22.9727

-7.3404

7.3404

-13.4574

7.3404

Gable Roof
Mansard Roof

-8.0201

4.6217

-13.4574

4.6217

-20.2540

4.6217

-8.6997

8.0201

-13.4574

7.3404

Hip Roof

-7.3404

4.6217

-12.7777

4.6217

-18.8947

4.6217

-8.6997

8.0201

-13.4574 '
7.3404

Monoslope Roof

-9.3794

3.9421

-12.0980

3.9421

-20.9337

3.9421

-8.6997

8.0201

-13.4574

7.3404

Flat Roof

-10.5831

-16.6114 !
NA

-22.6398

-7.2340

7.2340

-13.2623

7.2340

Gable Roof
Mansard Roof

-7.9038

4.5547

-13.2623

4.5547

-19.9605

4.5547

-8.5736

7.9038

-13.2623

7.2340

Hip Roof

-7.2340

4.5547

-12.5925

4.5547

-18.6209

4.5547

-8.5736

7.9038

-13.2623

7.2340

Monoslope Roof

-9.2435

3.8849

-11.9227

3.8849

-20.6303

3.8849

-8.5736

7.9038

-13.2623

7.2340

Flat Roof

-10.4274

-16.3671

-22.3068

-7.1276

7.1276

-13.0673

7.1276

Gable Roof
Mansard Roof

-7.7876

4.4878

-13.0673

4.4878

-19.6670

4.4878

-8.4476

7.7876

-13.0673

7.1276

Hip Roof

-7.1276

4.4878

-12.4073

4.4878

-18.3470

4.4878

-8.4476

7.7876

-13.0673

7.1276

Monoslope Roof

-9.1075

3.8278

*1 1.7474

3.8278

-20.3269

3.8278

-8.4476

7.7876

-13.0673

7.1276

Flat Roof

-10.1940

-16.0007

-21.8074

-6.9680

6.9680

-12.7748

6.9680

Gable Roof
Mansard Roof

-7.6132

4.3873

-12.7748

4.3873

-19.2267

4.3873

-8.2584

7.6132

-12.7748

6.9680

Hip Roof

-6.9680

4.3873

-12,1296

4.3873

-17.9363

4.3873

-8.2584

7.6132

-12.7748

6.9680

Monoslope Roof

-8.9036

3.7421

-11.4844

3.7421

-19.8718

3.7421

-8.2584

7.6132

-12.7748

6.9680

Association of Structural Engineers of the Philippines, Inc, (ASEP)

CHAPTER 2 - Minimum Design Loads 2-155

Part 5: Open Buildings

Commentary:

In determining loads on component and cladding elements
for open building roofs using Figures 207 E. 8-1, 207 E. 8-2
and 2 07 E. 8-3, it is important for the designer to note that
the net pressure coefficient C N is based on contributions
from the top and bottom surfaces of the roof This implies
that the element receives load from both surfaces. Such
would not be the case if the surface below the roof were
separated structurally from the top roof surface. In this
case, the pressure coefficient should be separated for the
effect of top and bottom pressures, or conservatively, each
surface could be designed using the C N value from Figures
207E.8-1, 207E.8-2 and207E.8-3.

207E.8 Building Types

The provisions of Section 207E.8 are applicable to an open
building of all heights having a pitched free roof,
monosloped free roof, or troughed free roof The steps
required for the determination of wind loads on
components and cladding for these building types is shown
in Table 207E.8-1.

207E.8.1 Conditions

For the determination of the design wind pressures on
components and claddings using the provisions of Section
207E.8.2, the conditions indicated on the selected figure(s)
shall be applicable to the building under consideration.

207E.8.2 Design Wind Pressures

The net design wind pressure for component and cladding
elements of open buildings of all heights with monoslope,
pitched, and troughed roofs shall be determined by the
following equation:

p = q h GC N (207E.8-1)

where

q h = velocity pressure evaluated at mean roof
height h using the exposure as defined in
Section 207A.7.3 that results in the highest
wind loads for any wind direction at the site
G = gust-effect factor from Section 207A.9
C N = net pressure coefficient given in:

• Figure 207E.8-1 for monosloped roof

• Figure 207E.8-2 for pitched roof

• Figure 207E.8-3 for troughed roof

Net pressure coefficients C N include contributions from top
and bottom surfaces. All load cases shown for each roof
angle shall be investigated. Plus and minus signs signify
pressure acting toward and away from the top surface of
the roof, respectively.

User Note:

Use Part 5 of Section 207 E for determining wind
pressures for C&C of open buildings having pitched,
monoslope or troughed roofs . These provisions are
based on the Directional Procedure with wind pressures
calculated from the specified equation applicable to
each roof surface.

Table 207E.8-1

Steps to Determine C&C Wind Loads
Open Buildings

Step 1: Determine risk category, see Table 103-1

Step 2: Determine the basic wind speed, V, for the
applicable risk category, see Figure 207A.5-
1A, BorC

Step 3: Determine wind load parameters:

> Wind directionality factor K zt ,
see Section 207 A.6 and Table 207A.6-1

> Exposure category B, C or D, see Section
207A.7

> Topographic factor K zt9 see Section
207A.8 and Figure 207A.8-1

> Gust effect factor, G, see Section 207A.9

Step 4 : Determine velocity pressure exposure
coefficient, K z or K h , see Table 207E.3-1

Step 5: Determine velocity pressure, q h ,

see Equation 207E.3-1

Step 6: Determine net pressure coefficients, C N

> Monosloped roof, see Figure 207E.8-1

> Pitched roof, see Figure 207E.8-2

> Troughed roof, see Figure 207E.8-3

Step 7 : Calculate wind pressure, p, see Equation
207E.8-1

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-156 CHAPTER 2 - Minimum Design Loads

Part 6: Building Appurtenances and Rooftop

Structures and Equipment

207E.9 Parapets

The design wind pressure for component and cladding
elements of parapets for all building types and heights,
except enclosed buildings with ft < 48 m for which the
provisions of Part 4 are used, shall be determined from the
following equation:

p = q p [(GC p ) - ( GC pi )] (207E.9-1)

where

q p = velocity pressure evaluated at the top of the
parapet

(GC p ) = external pressure coefficient given in

• Figure 207E.4-1 for walls with ft > 18 m

• Figures 207 E. 4-2 A to 207E.4-2C for flat
roofs, gable roofs, and hip roofs

• Figure 207E.4-3 for stepped roofs

• Figure 207E.4-4 for multispan gable roofs

• Figure 207E.4-5A and 207E.4-5B for
monoslope roofs

• Figure 207E.4-6 for sawtooth roofs

• Figure 207E.4-7 for domed roofs of all
heights

• Figure 207E.6-1 for walls and flat roofs
with ft > 18 m

• Figure 207B.4-3 for footnote 4 for arched
roofs

(GCpj) = internal pressure coefficient from
Table 207 A. 1 1-1, based on the porosity of the
parapet envelope

* Load Case B: Leeward Parapet shall consist of
applying the applicable positive wall pressure from
Figure 207E.4-1 (ft < 18 m) or Figure 207E.6-1
(ft > 18 m) to the windward surface of the parapet,
and applying the applicable negative wall pressure
from Figure 207E.4-1 (ft < 18 m) or Figure 207E.6-1
(ft > 18 m) as applicable to the leeward surface. Edge
and comer zones shall be arranged as shown in the
applicable figures. ( GC p ) shall be determined for
appropriate roof angle and effective wind area from
the applicable figures.

If internal pressure is present, both load cases should be
evaluated under positive and negative internal pressure.

The steps required for the determination of wind loads on
component and cladding of parapets are shown in Table
207E.9-1.

User Note:

Use Part 6 of Section 207E for determining wind
pressures for C&C on roof overhangs and parapets of
buildings. These provisions are based on the
Directional Procedure with wind pressures calculated
from the specified equation applicable to each roof
overhang or parapet surface.

Two load cases, see Figure 207E.9-1, shall be considered:

• Load Case A: Windward Parapet shall consist of
applying the applicable positive wall pressure from
Figure 207E.4-1 (ft < 18 m) or Figure 207E.6-1
(ft > 18 m) to the windward surface of the parapet
while applying the applicable negative edge or comer
zone roof pressure from Figures 207E.4-2 (A, B or C),
207E.4-3, 207E.4-4, 207E.4-5 (A or B), 207E.4-6,
207E.4-7, Figure 207B.4-3 footnote 4, or Figure
207E.6-1 (ft > 18 m) as applicable to the leeward
surface of the parapet.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-157

Table 207E.9-1

Steps to Determine C&C Wind Loads
Parapets

Step 1: Determine risk category, see Table 103-1

Step 2: Determine the basic wind speed, V, for the
applicable risk category, see Figure 207A.5-
1A, B or C

Step 3: Determine wind load parameters:

> Wind directionality factor K zt ,
see Section 207A.6 and Table 207A.6-1

> Exposure category B, C or D, see Section
207A.7

> Topographic factor K zt , see Section
207A.8 and Figure 207A.8-1

> Enclosure classification, see Section
207 A. 10

> Internal pressure coefficient, (GC p j), see
Section 207A.11 and Table 207A.11-1

Step 4: Determine velocity pressure exposure
coefficient, K h , at the top of the parapet see
Table 207E.3-1

Step 5: Determine velocity pressure, q p , at the top of
the parapet, see Equation 207E.3-1

Step 6: Determine external pressure coefficient for
wall and roof surfaces adjacent to parapet,
(GC P )

> Walls with h < 18 m, see Figure 207E.4-
1

> Flat, gable and hip roofs, see Figures
207E.4-2A to 207E.4.2C

> Stepped roofs, see Figure 207E.4-3

> Multispan gable roofs, see Figure
207E.4-4

> Monoslope roofs. Figures 207E.4-5A and
207E.4-5B

> Sawtooth roofs, see Figure 207E.4-6

> Domed roofs of all heights, see Figure
207E.4-7

> Walls and flat roofs with h > 18 m, see
Figure 207E.6-1

> Arched roofs, see footnote 4 of Figure
207B.4-3

Step 7: Calculate wind pressure, p, see Equation
207E.9-1 on windward and leeward face of
parapet, considering two load cases (Case A
and Case B) as shown in Figure 207E.9-1

207E.10 Roof Overhangs

The design wind pressure for roof overhangs of enclosed
and partially enclosed buildings of all heights, except
enclosed buildings with h < 48 m for which the provisions
of Part 4 are used, shall be determined from the following
equation:

p = q h [(GC p ) - (GC pi )] (N/m 2 ) (207E.10-1)

where

(GC P )

(GC P i)

velocity pressure from Section 207E.3.2
evaluated at mean roof height h using
exposure defined in Section 207A.7.3
external pressure coefficients for overhangs
given in Figures 207E.4-2A to 207E.4-2C (flat
roofs, gable roofs, and hip roofs), including
contributions from top and bottom surfaces of
overhang. The external pressure coefficient
for the covering on the underside of the roof
overhang is the same as the external pressure
coefficient on the adjacent wall surface,
adjusted for effective wind area, determined
from Figure 207E.4-1 or Figure 207E.6-1 as
applicable

internal pressure coefficient given in
Table 207A.11-1

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-158 CHAPTER 2 - Minimum Design Loads

The steps required for the determination of wind loads on
components and cladding of roof overhangs are shown in
Table 207E.10-1.

Table 207E.10-1

Steps to Determine C&C Wind Loads
Roof Overhangs

Step 1:

Determine risk category, see Table 103-1

Step 2;

Determine the basic wind speed, V, for the
applicable risk category, see Figure 207A.5-
1A, B or C

Step 3 :

Determine wind load parameters:

> Wind directionality factor K zt ,

see Section 207A.6 and Table 207A.6-1

> Exposure category B, C or D, see Section
207A.7

> Topographic factor ff zt , see Section
207 A.8 and Figure 207A.8-1

> Enclosure classification, see Section
207A.10

> Internal pressure coefficient, ( GC pi ),
see Section 207 A. 11 and

Table 207A.11-1

Step 4:

Determine velocity pressure exposure
coefficient, K h , see Table 207E.3-1

Step 5:

Determine velocity pressure, q h , at mean roof
height h using Equation 207E.3-1

Step 6:

Determine external pressure coefficient,
(GC p ), using Figures 207E.4-2A through C
for flat, gabled and hip roofs

Step 7:

Calculate wind pressure, p, using
Equation 207E. 10-1, refer to

Figure 207E.10-1

207E.11 Rooftop Structures and Equipment for
Buildings with h < 18 m

The components and cladding pressure on each wall of the
rooftop structure shall be equal to the lateral force
determined in accordance with Section 207D.5.1 divided
by the respective wall surface are of the rooftop structure
and shall be considered to act inward and outward. The
components and cladding pressure on the roof shall be
equal to the vertical uplift force determined in accordance
with Section 207D.5.1 divided by the horizontal projected
area of the roof of the rooftop structure and shall be
considered to act in the upward direction.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-159

-1.4

- 1.1

- 0.8

+0.7

+ 1.0

Notes:

1. Vertical scale denotes GC p to be used with q h .

2. Horizontal scale denotes effective wind area, m 2 .

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

4. Each component shall be designed for maximum positive and negative pressures.

5. Values of GC p for walls shall be reduced by 10% when 0 < 10° .

6. Notation:

a = 1 0% of least horizontal dimension or 0. 4ft, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.

ft - mean roof height, m, except that eave height shall be used for 9 < 10 ° .

0 = angle of plane of roof from horizontal, °

Figure 207E.4-1

External Pressure Coefficients, GC p Walls, h < 18 m Enclosed
Partially Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-160 CHAPTER 2 - Minimum Design Loads

<-W

c/1

c/i

0.1

0.9 1.9 4.6 9.3

Effective Wind Area, nf

18.6
2

46.5 92.9

-u

-01

0.1

0.9 1.9 4.6 9.3 18.6 46.5 92.9

Notes:

Effective Wind Area, m 2

2 .

Vertical scale denotes GC P to be used with q *.

Horizontal scale denotes effective wind area, m .

Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

Each component shall be designed for maximum positive and negative pressures.

If a parapet equal to or higher than 0.9 m is provided around the perimeter of the roof with 0 <7° , the negative values of GC p in Zone 3 shall be equal
to those for Zone 2 and positive values of GC p in Zones 2 and 3 shall be set equal to those for wall Zones 4 and 5 respectively in Figure 207E.4-1.

6 .

Values of GC P for roof overhangs include pressure contributions from both upper and lower surfaces.

Notation:

10% of least horizontal dimension or 0. 4 h, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.
eave height shall be used for 9 < 10 ° .
angle of plane of roof from horizontal, 0

Figure 207E.4-2A

External Pressure Coefficients, GC p Gable Roofs 6 < 7°, h < 18 m
Enclosed, Partially Enclosed Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-161

Notes:

* i-H

c/)

CZ)

i-H

■ t-H

C/3

0 l 0.9 1.9 4.6 9.3 18.6 46.5 92.9

Effective Wind Area, m 2

0.1 0.9 1.9 4.6 9.3 18.6 46.5 92.9

Effective Wind Area, m 2

1. Vertical scale denotes GC p to be used with q h .

2. Horizontal scale denotes effective wind area, m 2 .

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

4. Each component shall be designed for maximum positive and negative pressures.

5. Values of GC p for roof overhangs include pressure contributions from both upper and lower surfaces.

6. For hip roofs with 7 < 8 < 27°, edge/ridge strips and pressure coefficients for ridges of gabled roofs shall apply on each hip.

7. For hip roofs with 0 < 25 °, Zone 3 shall be treated as Zone 2.

8. Notation:

A =10% of least horizontal dimension or 0. 4h, whichever is smaller, but not less than either 4% of least horizontal dimension 0.9 m.

h ~ mean roof height, m, except that eave height shall be used for 0 < 10 ° .

9 = angle of plane of roof from horizontal, °

Figure 207E.4-2B

External Pressure Coefficients, GC p Gable/Hip Roofs 7° < 6 < 27°, h < 18 m
Enclosed, Partially Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-162 CHAPTER 2 - Minimum Design Loads

®& 3 )

Effective Wind Area, m 2

Overhang

Effective Wind Area, m 2

Notes:

Vertical scale denotes GC p to be used with q h .

Horizontal scale denotes effective wind area, m 2

Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

Each component shall be designed for maximum positive and negative pressures.

Values of GC p for roof overhangs include pressure contributions from both upper and lower surfaces.

Notation:

a = 1 0% of least horizontal dimension or 0 . 4 h, whichever is smaller, but not less than either 4% of least horizontal dimension 0 9

h = mean roof height, m

6 — angle of plane of roof from horizontal, °

Figure 207E.4-2C

External Pressure Coefficients, GC p Gable Roofs 27° < 6 < 45°, ft < 18 m
Enclosed, Partially Enclosed Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

Roof

r — 1

— ■

—

CHAPTER 2 - Minimum Design Loads 2-163

h x > 3 m
b = 1.5/h
b < 30 m

— = 0.30 to 0.70
h

0.25 to 0.75
w

Notes:

I On the lower level of flat, stepped roofs shown in Figure 207E.4-3, the zone designations and pressure coefficients shown in Figure 207E.4-2A shall
apply, except that at the roof-upper wall intersection(s), Zone 3 shall be treated as Zone 2 and Zone 2 shall be treated as Zone 1 . Positive values of GC V
equal to those for walls in Figure 207E.4-1 shall apply on the cross-hatched areas shown in Figure 207E.4-3,

2. Notation:

b =1. 5/ii in Figure 207E.4-3, but not greater than 30 m.
h = mean roof height, m

h t = hi or h 2 in Figure 207E.4-3; h = + h 2 \ >3.1 m; hrfh = 0. 3 to 0. 7.

W = Building width in Figure 207E.4-3.

W t = Wx or W 2 or W 3 in Figure 207E.4-3. W = W 1 + W 2 orW 1 + W 2 + W 3 ; WJW = 0. 25 to 0. 75.

0 = Angle of plane of roof from horizontal, °

Figure 207E.4-3

External Pressure Coefficients, GC p Stepped Roofs, h < 18 m
Enclosed, Partially Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-164 CHAPTER 2 - Minimum Design Loads

-3.0

- 2.8

_ - 2.6
Ph

O -2-4

O -2-2

- 2.0

- 1.8

- 1.6

P
• Sh

o -> 2
U-i.o
£ - 0.8
3

C/3
8 -°- 4
£ - 0 - 2

-a o

e +o - 2

(D +0.4
X! +0.6

^ + 0.8
0.1

- 0.6

(3)

10 c

< 6

S 30°

—

^TX2)^3'I

—

— ~

—

0.9 1.9

4.6 9.3 18.6 46.5 92.9

Effective Wind Area, m 2

1. Vertical scale denotes GC p to be used with q h .

0.1

0.9 1.9 4.6

2 .

6 .

Horizontal scale denotes effective wind area A, m 2

9.3 18.6

46.5 92.9

Effective Wind Aros m

Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. ?

Each component shall be designed for maximum positive and negative pressures.

For 0 < 10°, values of GC p from Figure 207E.4-2A shall be used.

Notation:

a = 1 0% of least horizontal dimension or 0. 4 h, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.

h = mean roof height, m, except that the eave height shall be used for 0 < 10 °

W = building module width, m

0 = angle of plane of roof from horizontal, °

Figure 207E.4-4

External Pressure Coefficients, GC p Multispan Gable Roofs, h < 18 m
Enclosed, Partially Enclosed Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-165

r 2o i

0.1

0.9 1.9

Effective Wind Area, m 2

- 2.6

- 1.8

- 1.6
-I 5

-1.3

- 1.2

- 1.1

+0 2
+0.3

4.6 9.3 18.6 46.5 92.9

Notes:

1 . Vertical scale denotes GC p to be used with q h .

2. Horizontal scale denotes effective wind area A, m 2

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

4. Each component shall be designed for maximum positive and negative pressures.

5. For 6 < 3°, values of GC p from Figure 207E.4-2A shall be used.

6. Notation:

a - 10% of least horizontal dimension or 0.4fc, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.

h = eave height shall be used for 0 < 10°

W = building width, m
6 - angle of plane of roof from horizontal, °

Figure 207E.4-5A

External Pressure Coefficients, GC p Monoslope Roofs, 3° < 6 < 10 °, h < 18 m
Enclosed, Partially Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-166 CHAPTER 2 - Minimum Design Loads

Notes:

1 . Vertical scale denotes GC p to be used with q h .

2. Horizontal scale denotes effective wind area A , m 2

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

4. Each component shall be designed for maximum positive and negative pressures.

5. Notation:

a = 10% of least horizontal dimension or 0. 4 h, whichever is smaller, but not less than either 4% of least horizontal dimension 0.9 m

h = mean roof height, m

W = building width, m

0 = angle of plane of roof from horizontal, °

Figure 207E.4-5B

External Pressure Coefficients, GC p Monoslope Roofs, 10° < 0 < 30°, h < 18 m
Enclosed, Partially Enclosed Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

I _ tv

CHAPTER 2 - Minimum Design Loads

2-167

1. Vertical scale denotes GC p to be used with q h .

2. Horizontal scale denotes effective wind area A , m 2

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

4. Each component shall be designed for maximum positive and negative pressures.

5. For 6 < 10°, values of GC p from Figure 207E.4-2A shall be used.

6. Notation:

a = 10% of least horizontal dimension or 0. Ah, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.

h = mean roof height, m, except that the eave height shall be used for 0 < 10°

W = building module width, m

6 = angle of plane of roof from horizontal, °

Figure 207E.4-6

External Pressure Coefficients, GC p Sawtooth Roofs, h < 18 m
Enclosed, Partially Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-168 CHAPTER 2 - Minimum Design Loads

External Pressure Coefficient for Domes with a Circular Base

9 , degrees

Negative Pressures

Positive Pressures

0-90

0-60

61-90

GCp

-0.90

+0.90

+0.50

Notes:

1 . Values denote GC p to be used with g (/li)+/) , where h D + / is the height at the top of the dome.

2. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

3. Each component shall be designed for maximum positive and negative pressures.

4. Values apply to 0 < h D /D < 0 . 5 , 0 . 2 < f/D < 0 . 5 .

5. 0 = 0 ° on dome springline, 9 = 90 ° at dome center top point. / is measured from spring line to top.

Figure 207E.4-7

External Pressure Coefficients, GC p Doomed Roofs, All Heights
Enclosed, Partially Enclosed Buildings and Structures

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-169

I I Interior Zones End Zones ^HCorner Zones

Roofs - Zone 1/Walls - Zone 4 Roofs - Zone 2/Walls - Zone 5 Roofs - Zone 3

Notes:

1 . Pressures shown are applied normal to the surface, for exposure B, at h = 9 m. Adjust to other conditions using Equation 207E.5- 1 .

2. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively.

3. For hip roofs with 0 < 25°, Zone 3 shall be treated as Zone 2.

4. For effective wind areas between those given, value may be interpolated, otherwise use the value associated with the lower effective wind area.

5. Notation:

a =* 10% of least horizontal dimension or 0. 4Ji, whichever is smaller, but not less than either 4% of least horizontal dimension or 0.9 m.

h = mean roof height, m, except that the eave height shall be used for 6 < 10°

0 — angle of plane of roof from horizontal, °

Figure 207E.5-1

Design Wind Pressures Walls and Roofs, h < 18 m
Enclosed Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

Wall Roof > 27 to 45 degrees Roof >7 to 27 degrees Roof 0 to 7 degrees

2-170 CHAPTER 2 - Minimum Design Loads

Net Design Wind Pressure, p net (kPa) (Exposure B at h, = 10 m with / — 1.0 and K d — 1.0)

-1

.50

-1

.38

-1

.10

Note: For effective areas between those given above the load may be interpolated, otherwise use the load associated with the lower effective

area . The final value, including all permitted reductions, used in the design shall not be less than that required by Section 207E.2.2.

Figure 207E.5-1 (continued)

Design Wind Pressures on Walls and Roofs of Enclosed Buildings with h < 18 m

Components and Cladding

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-171

Roof Overhang Net Design Wind Pressure, p net (kPa)
(Exposure B at h = 10 m with / = 1.0 and K d = 1.0)

Zone

Effective

wind

area

(sq.m)

Basic Wind Speed V (kph)

150

200

250

300

350

0 i

0.9

- 1.19

- 2.12

- 3.31

- 4.76

- 6.48

1.9

- 1.17

- 2.08

- 3.25

- 4.69

- 10.27

4.6

- 1.14

- 2.03

- 3.17

- 4.57

- 6.38

9.3

- 1.13

- 2.00

- 3.13

- 4.51

- 8.21

-'M

0.9

- 1.89

- 3.35

- 5.24

- 7.55

- 6.22

1.9

- 1.51

- 2.68

- 4,19

- 6.03

- 5.45

4.6

- 1.00

- 1.78

- 2.78

- 4.00

- 6.14

9.3

- 1.25

- 2.23

- 3.48

- 5.02

- 6.83

0.9

- 1.51

- 2.68

- 4.19

- 6.03

- 8.21

0JD

1.9

- 1.51

- 2.68

- 4.19

- 6.03

- 13.38

4.6

- 1.51

- 2.68

- 4.19

- 6.03

- 8.21

9.3

- 1.51

- 2.68

- 4.19

- 6.03

- 12.17

0.9

- 2.46

- 4.37

- 6.82

- 9.83

- 8.21

1.9

- 2.24

- 3.97

- 6.21

- 8.94

- 10.45

4.6

- 1.92

- 3.41

- 5.33

- 7.67

- 8.21

9.3

- 1.70

- 3.02

- 4.71

- 6.79

- 9.24

0.9

- 1.38

- 2.45

- 3.83

- 5.52

- 7.52

b£

1.9

- 1.35

- 2.40

- 3.75

- 5.40

- 7.52

4.6

- 1.29

- 2.29

- 3.57

- 5.14

- 7.34

9.3

- 1.25

- 2.23

- 3.48

- 5.02

- 7.34

0.9

- 1.38

- 2.45

- 3.83

- 5.52

- 7.00

1.9

- 1.35

- 2.40

- 3.75

- 5.40

- 7.00

«4— 1

4.6

- 1.29

- 2.29

- 3.57

- 5.14

- 6.83

9.3

- 1.25

- 2.23

- 3.48

- 5.02

- 6.83

Adjustment Factor
for Building Height and Exposure, A

Mean roof height
(m)

Exposure

4.5

1.00

1.21

1.47

6.0

1.00

1.29

1.55

7.5

1.00

1.35

1.61

9.0

1.00

1.40

1.66

10.5

1.05

1.45

1.70

12.0

1.09

1.49

1.74

13.5

1.12

1.53

1.78

15.0

1.16

1.56

1.81

16.5

1.19

1.59

1.84

18.0

1.22

1.62

1.87

Figure 207E.5-1 (continued)

Design Wind Pressures on Walls and Roofs of Enclosed Buildings with h < 18 m

Components and Cladding

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-172

CHAPTER 2 - Minimum Design Loads

WALL ELEVATION

Notes:

1 .

2 .

3 .

6 .

8 .

Vertical scale denotes GC„ to he used with appropriate q, or q h .

Missis's - t ^ respectiveiy -

Use rt with positive values of CC„ and q h with negative values of GC„.

ssr iif.3 - «, — *-*- « - c - — *

ffTXm” ^id«l around the P .,l-,«r of ft. roof with » < 10" , Zo.e ) shah he «.,.d a, Z.ue 2.

Notation:

1 0% of least horizontal dimension, but not less than 0.9 m.

mean rooflwighl, Jtt, except that cave height shall be used for 6 _ 1 •

he i glu above ground, ni

angle of plane of roof from horizontal, °

Figure 207E.6-1

External Pressure Coefficients, GC p Walls and Roofs, h > 18 m
Enclosed, Partially Enclosed Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-1

Windward parapet Leeward parapet

Load Case A Load Case B

Top parapet

Windward Parapet

Load Case A

L Windward parapet pressure (p t ) is determined using the positive wall pressure (p 5 ) zones 4 or 5 from Table 207E.7-2.
2. Leeward parapet pressure (p 2 ) is determined using the negative roof pressure (p 7 ) zones 2 or 3 from Table 207E.7-2.

Leeward Parapet

Load Case B

1 . Windward parapet pressure (p 3 ) is determined using the positive wall pressure (p 5 ) zones 4 or 5 from Table 207E.7-2.

2. Leeward parapet pressure (p 4 ) is determined using the negative wall pressure (p 6 ) zones 4 or 5 from Table 207E.7-2.

Figure 207E.7-1

Parapet Wind Loads Application of Parapet Wind Loads, h < 48.8 m
Enclosed Simple Diaphragm Buildings

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-174 CHAPTER 2 - Minimum Design Loads

Vovh ~ 1-0 x roof pressure p from tables for edge Zones 1, 2

Povh ~ 1 . 1 5 x roof pressure p from tables for comer Zone 3

Notes:

1 • Povh ~ roof pressure at overhang for edge or comer zone as applicable from figures in roof pressure table.

2. Povh fr° m figures includes load from both top and bottom surface of overhang.

3. Pressure p s at soffit of overhang can be assumed same as wall pressure, p w .

Figure 207E.7-2

Roof Overhang Wind Loads Application of Overhang Wind Loads, h < 48
Enclosed Simple Diaphragm Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design I oads

2-175

Roof

Angle

Effective
Wind Area

Clear Wind Flow

Obstructed Wind Flow

Zone 3

Zone 2

Zone 1

Zone 3

Zone 2

Zone 1

0°

< 3 2

2.4

-3.3

1.8

-1.7

1.2

-1.1

-3.6

0.8

-1.8

0.5

-1.2

> a 2 ,

< 4.0a 2

1.8

-1.7

1.8

-1.7

1.2

-1.1

0.8

-1.8

0.8

-1.8

0.5

-1.2

> 4.0a 2

1.2

-1.1

1.2

-1.1

1.2

-1.1

0.5

-1.2

0.5

-1.2

0.5

-1.2

7.5°

< a 2

3.2

-4.2

2.4

-2.1

1.6

-1.4

1.6

-5.1

1.2

-2.6

0.8

-1.7

> a 2 ,

< 4.0a 2

2.4

-2.1

2.4

-2.1

1.6

-1.4

1.2

-2.6

1.2

-2.6

0.8

-1.7

> 4.0a 2

1.6

-1.4

1.6

-1.4

1.6

-1.4

0.8

-1.7

0.8

-1.7

0.8

-1.7

15°

< a 2

3.6

-3.8

2.7

-2.9

1.8

-1.9

2.4

-4.2

1.8

-3.2

1.2

-2.1

> a 2 ,

< 4.0a 2

2.7

-2.9

2.7

-2.9

1.8

-1.9

1.8

-3.2

1.8

-3.2

1.2

-2.1

> 4.0a 2

1.8

-1.9

1.8

-1.9

1.8

-1.9

1.2

-2.1

1.2

-2.1

1.2

-2.1

30°

< a 2

5.2

-5

3.9

-3.8

2.6

2.5

3.2

-4.6

2.4

-3.5

1.6

-2.3

> a 2 ,

< 4.0a 2

3.9

-3.8

3.9

-3.8

2.6

2.5

2.4

-3.5

2.4

-3.5

1.6

-2.3

> 4.0a 2

2.6

-2.5

2.6

-2.5

2.6

2.5

1.6'

-2.3

1.6

-2.3

1.6

-2.3

45°

< a 2

5.2

-4.6

3.9

-3.5

2.6

2.3

4.2

-3.8

3.2

-2.9

2.1

-1.9

> a 2 ,

< 4.0a 2

3.9

-3.5

3.9

-3.5

2.6

2.3

3.2

-2.9

3.2

-2.9

2.1

-1.9

> 4.0a 2

2.6

-2.3

2.6

-2.3

2.6

2.3

2.1

-1.9

2.1

-1.9

2.1

-1.9

Notes:

1. C N denotes net pressures (contributions from top and bottom surfaces).

2. Clear wind flow denotes relatively unobstructed wind flow with blockage less than or equal to 50%. Obstructed wind flow denotes objects below roof
inhibiting wind flow (>50% blockage).

3. For values of 6 other than those shown, linear interpolation is permitted.

4. Plus and minus signs signify pressures acting towards and away from the top roof surface, respectively.

5. Components and cladding elements shall be designed for positive and negative pressure coefficients shown.

6. Notation:

a = 10% of least horizontal dimension or 0.4/i, whichever is smaller but not less than 4% of least horizontal dimension or 0.9 m.

h ' m mean roof height, m

L — Horizontal dimension of building, measured in along wind direction, m

8 ~ angle of plane of roof from horizontal, °

Figure 207E.8-1

Net Pressure Coefficient, C N Monoslope Free Roofs, 6 < 45°, 0.25< h/L < 1.0

Open Buildings

National Structural Code of the Philippines Volume l p 7th Edition, 2015

2-176 CHAPTER 2 - Minimum Design Loads

777777777777777777777

Roof

Effective

4 - ~~1

Angle

Wind Area

Clear Wind Flow

Obstructed Wind Flow

Zone 3

Zone 2

Zone 1

Zone 3

Zor

ie 2

Zor

ie 1

< a 2

2.4

- 3.3

1.8

- 1.7

1.2

- 1.1

- 3.6

0.8

- 1.8

0.5

- 1.2

0 °

> a 2 ,

< 4 . 0a 2

1.8

- 1.7

1.8

- 1.7

1.2

- 1.1

0.8

- 1.8

0.8

- 1.8

0.5

- 1.2

> 4 . 0a 2

1.2

- 1.1

1.2

- 1.1

1.2

- 1.1

0.5

- 1.2

0.5

- 1.2

0.5

- 1.2

< a 2

2.2

- 3.6

1.7

- 1.8

1.1

- 1.2

- 5.1

0.8

- 2.6

0.5

- 1.7

7.5°

> a 2 ,

< 4 . 0a 2

1.7

- 1.8

1.7

- 1.8

1.1

- 1.2

0.8

- 2.6

0.8

- 2.6

0.5

- 1.7

> 4 . 0a 2

i.i

- 1.2

1.2

- 1.2

1.1

- 1.2

0.5

- 1.7

0.5

- 1.7

0.5

- 1.7

< a 2

2.2

- 2.2

1.7

- 1.7

i.i

- 1.1

- 3.2 :

0.8

- 2.4

0.5

- 1.6

15°

> a 2 ,

< 4 . 0a 2

1.7

- 1.7

1.7

- 1.7

i.i

- 1.1

0.8

- 2.4

0.8

- 2.4

0.5

- 1.6

> 4 . 0a 2

1.1

- 1.1

1.1

- 1.1

1.1

- 1.1

0.5

- 1.6

0.5

- 1.6

0.5

- 1.6

< a 2

2.6

- 1.8

- 1.4

1.3

- 0.9

- 2.4

0.8

- 1.8

0.5

- 1.2

30°

> a 2 ,

< 4 . 0a 2

- 1.4

1.3

- 0.9

0.8

- 1.8

0.8

- 1,8

0.5

- 1.2

> 4 . 0a 2

1.3

- 0.9

1.3

- 0.9

1.3

- 0.9

0.5

- 1.2

0.5

- 1.2

0.5

- 1.2

< a 2

2.2

- 1.6

1.7

- 1.2

1.1

- 0.8

- 2.4

0.8

- 1.8

0.5

- 1.2

45°

> a 2 ,

< 4 . 0a 2

1.7

- 1.2

1.7

- 1.2

1.1

- 0.8

- 1.8

0.8

- 1.8

0.5

- 1.2

> 4 . 0a 2

1.1

- 0.8

1.1

- 0.8

1.1

- 0.8

0.5

- 1.2

0.5

- 1.2

0.5

- 1.2

Notes:

1 . C N denotes net pressures (contributions from top and bottom surfaces).

2. Clear wind flow denotes relatively unobstructed wind flow with blockage less than or equal to 50%. Obstructed wind flow denotes objects below roof
inhibiting wind flow (>50% blockage).

3. For values of 0 other than those shown, linear interpolation is permitted.

4. Plus and minus signs signify pressures acting towards and away from the top roof surface, respectively.

5. Components and cladding elements shall be designed for positive and negative pressure coefficients shown.

6. Notation:

a = 1 0% of least horizontal dimension or 0. 4 h, whichever is smaller but not less than 4% of least horizontal dimension or 0.9 m. Dimension

“a” is as shown in Figure 207E.8-1.
h = mean roof height, m

L Horizontal dimension of building, measured in along wind direction, m

0 = angle of plane of roof from horizontal, °

Figure 207E . 8-2

Net Pressure Coefficient , C N Pitched Free Roofs , 6 < 45 °, 0 . 25 < h/L < 1.0

Open Buildings

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-177

0 > 10 °

Roof

Angle

Effective
Wind Area

Clear Wind Flow

Obstructed Wind Flow

Zone 3

Zone 2

Zone 1

Zone 3

Zone 2

Zone 1

0°

< a 2

2.4

- 3.3

1.8

- 1.7

1.2

- 1.1

- 3.6

0.8

- 1.8

0.5

- 1.2

> a 2 ,

< 4.0a 2

1.8

- 1.7

1.8

- 1.7

1.2

- 1.1

0.8

- 1.8

0.8

- 1.8

0.5

- 1.2

> 4.0a 2

1.2

- 1.1

1.2

- 1.1

1.2

- 1.1

0.5

- 1.2

0.5

- 1.2

0.5

- 1.2

7 . 5 °

< a 2

2.4

- 3.3

1.8

- 1.7

1.2

- 1.1

- 4.8

0.8

- 2.4

0.5

- 1.6

> a 2 ,

< 4.0a 2

1.8

- 1.1

1.8

- 1.7

1.2

- 1.1

0.8

- 2.4

0.8

- 2.4

0.5

- 1.6

> 4.0a 2

1.2

- 1.1

1.2

- 1.1

1.2

- l.i

0.5

- 1.6

0.5

- 1.6

0.5

- 1.6

15°

< a 2

2.2

- 2.2

1.7

- 1.7

1.1

- 1.1

- 2.4

0.8

- 1.8

0.5

- 1.2

> a 2 ,

< 4.0a 2

1.7

- 1.7

1.7

- 1.7

1.1

- l.i

0.8

- 1.8

0.8

- 1.8

0.5

- 1.2

> 4.0a 2

1.1

- 1.1

1.1

- 1.1

1.1

- l.i

0.5

- 1.2

0.5

- 1.2

0.5

- 1.2

30°

< a 2

1.8

- 2.6

1.4

-2

0.9

- 1.3

- 2.8

0.8

- 2.1

0.5

- 1.4

> a 2 ,

< 4.0a 2

1.4

-2

1.4

-2

0.9

- 1.3

0 . 8 .

- 2.1

0.8

- 2.1

0.5

- 1.4

> 4.0a 2

0.9

- 1.3

0.9

- 1.3

0.9

- 1.3

0.5

- 1.4

0.5

- 1.4

0.5

- 1.4

45°

< a 2

1.6

- 2.2

1.2

- 1.7

0.8

- 1.1

- 2.4

0.8

- 1.8

0.5

- 1.2

> a 2 ,

< 4.0a 2

1.2

- 1.7

1.2

- 1.7

0.8

- 1.1

0.8

- 1.8

0.8

- 1.8

0.5

- 1.2

> 4.0a 2

0.8

- 1.1

0.8

- 1.1

0.8

- 1.1

0.5

- 1.2

0.5

- 1.2

0.5

- 1.2

Notes:

1 . C N denotes net pressures (contributions from top and bottom surfaces).

2. Clear wind flow denotes relatively unobstructed wind flow with blockage less than or equal to 50%. Obstructed wind flow denotes objects below roof
inhibiting wind flow (>50% blockage).

3. For values of 9 other than those shown, linear interpolation is permitted.

4. Plus and minus signs signify pressures acting towards and away from the top roof surface, respectively.

5. Components and cladding elements shall be designed for positive and negative pressure coefficients shown.

6. Notation:

a — 10% of least horizontal dimension or 0.4h, whichever is smaller but not less than 4% of least horizontal dimension or 0,9 m.

Dimension “a” is as shown in Figure 207E.8-1.
h ~ mean roof height, m

L — Horizontal dimension of building, measured in along wind direction, m
9 ~ angle of plane of roof from horizontal, °

Figure 207E.8-3

Net Pressure Coefficient, C N Troughed Free Roofs, 0 < 45°, 0.25< h/L < 1.0

Open Buildings

National Structural Code of the Philippines Volume I , 7th Edition , 2015

2-178

CHAPTER 2 - Minimum Design Loads

Windward parapet
Load Case A

Leeward parapet

Load Case B Top parapet

Load Case A

1 . Windward parapet pressure ( p 1 ) is determined using the positive wall pressure (p 5 ) zones 4 or 5 from the applicable figure.

2. Leeward parapet pressure (p 2 ) is determined using the negative roof pressure (p 7 ) zones 2 or 3 from the applicable figure.

Leeward Parapet

Load Case B

1 . Windward parapet pressure (p 3 ) is determined using the positive wall pressure (p 5 ) zones 4 or 5 from the applicable figure.

2. Leeward parapet pressure (p 4 ) is determined using the negative wall pressure (p 6 ) zones 4 or 5 from the applicable figure.

User Note:

See Note 5 in Figure 207 E. 4-2 A and Note
7 in Figure 207E.6-1 for reductions in
component and cladding roof pressures
when parapets 0.9 m or higher are
present.

Figure 207E.9-1

Parapet Wind Loads C&C - Part 6, All Building Heights All Building Types

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-179

Notes:

1 . Net roof pressure p orft on roof overhangs is determined from interior, edge or comer zones as applicable from figures.

2. Net pressure p ovh from figures includes pressure contribution from top and bottom surfaces of roof overhang.

3. Positive pressure at roof overhang soffit p s is the same as adjacent wall pressure p w .

Figure 207E.10-1

Wind Loading - Roof Overhangs, C&C, All Building Heights All Building Types

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-180 CHAPTER 2- Minimum Design Loads

207F Wind Tunnel Procedure

Wind tunnel testing is specified when a structure contains
any of the characteristics defined in Sections 207B.1.3,
207C.1.3, 207D.1.3, or 207E.1.3 or when the designer
wishes to more accurately determine the wind loads. For
some building shapes wind tunnel testing can reduce the
conservatism due to enveloping of wind loads inherent in
the Directional Procedure , Envelope Procedure , or
Analytical Procedure for Components and Cladding. Also ,
wind tunnel testing accounts for shielding or channeling
and can more accurately determine wind loads for a
complex building shape than the Directional Procedure,
Envelope Procedure, or Analytical Procedure for
Components and Cladding. It is the intent of the code that
any building or other structure be allowed to use the wind
tunnel testing method to determine wind loads.
Requirements for proper testing are given in Section
207F.2.

It is common practice to resort to wind tunnel tests when
design data are required for the following wind- induced
loads:

1. Curtain wall pressures resulting from irregular
geometry.

2. Across-wind and/or torsional loads.

3. Periodic loads caused by vortex shedding.

4. Loads resulting from instabilities, such as flutter or
galloping.

Boundary-layer wind tunnels capable of developing flows
that meet the conditions stipulated in Section 207 F. 2
typically have test-section dimensions in the following
ranges: width of 2 to 4 m, height of 2 to 3 m, and length of
15 to 30 m. Maximum wind speeds are ordinarily in the
range of 10 to 45 m/s. The wind tunnel may be either an
open-circuit or closed circuit type.

Three basic types of wind-tunnel test models are commonly
used. These are designated as follows: (1) rigid Pressure
Model (PM), (2) rigid high-frequency base balance model
(H-FBBM), and (3) Aero-elastic Model (AM). One or more
of the models may be employed to obtain design loads for
a particular building or structure. The PM provides local
peak pressures for design of elements, such as cladding
and mean pressures, for the determination of overall mean
loads. The H-FBBM measures overall fluctuating loads
(aerodynamic admittance) for the determination of
dynamic responses. When motion of a building or structure
influences the wind loading, the AM is employed for direct
measurement of overall loads, deflections, and

accelerations. Each of these models, together with a model
of the surroundings (proximity model), can provide
information other than wind loads, such as snow loads on
complex roofs, wind data to evaluate environmental impact
on pedestrians, and concentrations of air-pollutant
emissions for environmental impact determinations.
Several references provide detailed information and
guidance for the determination of wind loads and other
types of design data by wind tunnel tests (Cermak 1977,
Reinhold 1982, ASCE 1999, and Boggs andPeterka 1989).

Wind tunnel tests frequently measure wind loads that are
significantly lower than required by Sections 207 A, 207 B,
207 C, 207 D, and 207 E due to the shape of the building, the
likelihood that the highest wind speeds occur at directions
where the building ’s shape or pressure coefficients are less
than their maximum values, specific buildings included in
a detailed proximity model that may provide shielding in
excess of that implied by exposure categories, and
necessaiy conservatism in enveloping load coefficients in
Sections 207C and 207E. In some cases, adjacent
structures may shield the structure sufficiently that
removal of one or two structures could significantly
increase wind loads. Additional wind tunnel testing without
specific nearby buildings (or with additional buildings if
they might cause increased loads through channeling or
buffeting) is an effective method for determining the
influence of adjacent buildings.

For this reason, the code limits the reduction that can be
accepted from wind tunnel tests to 80 percent of the result
obtained from Part 1 of Section 207B or Part 1 of Section
207C, or Section 207E, if the wind tunnel proximity model
included any specific influential buildings or other objects
that, in the judgment of an experienced wind engineer, are
likely to have substantially influenced the results beyond
those characteristic of the general surroundings. If there
are any such buildings or objects, supplemental testing can
be performed to quantify their effect on the original results
and possibly justify a limit lower than 80 percent, by
removing them from the detailed proximity model and
replacing them with characteristic ground roughness
consistent with the adjacent roughness. A specific
influential building or object is one within the detailed
proximity model that protrudes well above its
surroundings, or is unusually close to the subject building,
or may otherwise cause substantial sheltering effect or
magnification of the wind loads. When these supplemental
test results are included with the original results, the
acceptable results are then considered to be the higher of
both conditions.

However, the absolute minimum reduction permitted is 65
percent of the baseline result for components and cladding,
and 50 percent for the main wind force resisting system. A
higher reduction is permitted for MWFRS, because

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

J-1.fi 1

components and cladding loads are more subject to
changes due to local channeling effects when surroundings
change and can easily be dramatically increased when a
new adjacent building is constructed. It is also recognized
that cladding failures are much more common than failures
of the MWFRS . In addition , for the case of MWFRS it is
easily demonstrated that the overall drag coefficient for
certain common building shapes, such as circular
cylinders especially with rounded or domed tops, is one-
half or less of the drag coefficient for the rectangular
prisms that form the basis of Section 207B, 207 C, and
207 E.

For components and cladding, the 80-percent limit is
defined by the interior zones 1 and 4 in Figures 207E.4-1,
207E.4-2A, 207 E. 4-2 B, 207E.4-2C, 207E.4-3, 207E.4-4,
207 E. 4-5 A, 207E.4-5B, 207E.4-6, 207E.4-7, and 207 E. 5-

1. This limitation recognizes that pressures in the edge
zones are the ones most likely to be reduced by the specific
geometry* of real buildings compared to the rectangular
prismatic buildings assumed in Section 207 E. Therefore,
pressures in edge and corner zones are permitted to be as
low as 80 percent of the interior pressures from Section
207E without the supplemental tests . The 80 percent limit
based on zone 1 is directly applicable to all roof areas, and
the 80 percent limit based on zone 4 is directly applicable
to all wall areas.

The limitation on MWFRS loads is more complex because
the load effects (e.g., member stresses or forces,
deflections) at any point are the combined effect of a vector
of applied loads instead of a simple scalar value. In general
the ratio of forces or moments or torques (force
eccentricity) at various floors throughout the building
using a wind tunnel study will not be the same as those
ratios determined from Sections 207 B and 207C, and
therefore comparison between the two methods is not well
defined. Requiring each load effect from a wind tunnel test
to be no less than 80 percent of the same effect resulting
from Sections 207B and 207 C is impractical and
unnecessarily complex and detailed, given the approximate
nature of the 80 percent value. Instead, the intent of the
limitation is effectively implemented by applying it only to
a simple index that characterizes the overall loading. For
flexible (tall) buildings, the most descriptive index of
overall loading is the base overturning moment. For other
buildings, the overturning moment can be a poor
characterization of the overall loading, and the base shear
is recommended instead '.

207F.1 Scope

The Wind Tunnel Procedure shall be used where required
by Sections 207B.1.3, 207C.1.3, and 207D. 1.3. The Wind
Tunnel Procedure shall be permitted for any building or
structure in lieu of the design procedures specified in
Section 207B (MWFRS for buildings of all heights and
simple diaphragm buildings with h < 49 m, Section 207C
(MWFRS of low-rise buildings and simple diaphragm low-
rise buildings), Section 207D (MWFRS for all other
structures), and Section 207E (components and cladding
for all building types and other structures).

User Note;

Section 207F may always be used for determining wind
pressures for the MWFRS and/or for C&C of any
building or structure. This method is considered to
produce the most accurate wind pressures of any
method specified in this Code.

207F.2 Test Conditions

Wind tunnel tests, or similar tests employing fluids other
than air, used for the determination of design wind loads
for any building or other structure, shall be conducted in
accordance with this section. Tests for the determination of
mean and fluctuating forces and pressures shall meet all of
the following conditions:

1. The natural atmospheric boundary layer has been
modeled to account for the variation of wind speed
with height.

2. The relevant macro-(integral) length and micro-length
scales of the longitudinal component of atmospheric
turbulence are modeled to approximately the same
scale as that used to model the building or structure.

3. The modeled building or other structure and
surrounding structures and topography are
geometrically similar to their full-scale counterparts,
except that, for low-rise buildings meeting the
requirements of Section 207C.1.2, tests shall be
permitted for the modeled building in a single
exposure site as defined in Section 207 A. 7. 3.

4. The projected area of the modeled building or other
structure and surroundings is less than 8 percent of the
test section cross-sectional area unless correction is
made for blockage.

5. The longitudinal pressure gradient in the wind tunnel
test section is accounted for.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-182 CHAPTER 2 - Minimum Design Loads

6. Reynolds number effects on pressures and forces are
minimized.

7. Response characteristics of the wind tunnel
instrumentation are consistent with the required
measurements.

207F.3 Dynamic Response

Tests for the purpose of determining the dynamic response
of a building or other structure shall be in accordance with
Section 207F.2. The structural model and associated
analysis shall account for mass distribution, stiffness, and
damping.

207F.4 Load Effects

207F.4.1 Mean Recurrence Intervals of Load Effects

The load effect required for Strength Design shall be
determined for the same mean recurrence interval as for the
Analytical Method, by using a rational analysis method,
defined in the recognized literature, for combining the
directional wind tunnel data with the directional
meteorological data or probabilistic models based thereon.
The load effect required for Allowable Stress Design shall
be equal to the load effect required for Strength Design
divided by 1.6. For buildings that are sensitive to possible
variations in the values of the dynamic parameters,
sensitivity studies shall be required to provide a rational
basis for design recommendations.

Commentary:

Examples of analysis methods for combining directional
wind tunnel data with the directional meteorological data
or probabilistic models based thereon are described in
Lepage and Irwin (1985), Rigato etal. (2001), Isyumov et
al. (2003), Irwin et al (2005), Simiu and Filliben (2005),
and Simiu and Miyata (2006).

207F.4.2 Limitations on Wind Speeds

The wind speeds and probabilistic estimates based thereon
shall be subject to the limitations described in Section
207A.5.3.

Commentary:

Section 207F.4.2 specifies that the statistical methods used
to analyze historical wind speed and direction data for
wind tunnel studies shall be subject to the same limitations
specified in Section 207 F. 4. 2 that apply to the Analytical
Method.

Database-Assisted Design. Wind-tunnel aerodynamics
databases that contain records of pressures measured
synchronously at large numbers of locations on the
exterior surface of building models have been developed by
wind researchers, e.g., Simiu et al. (2003) and Main and
Fritz (2006). Such databases include data that permit a
designer to determine, without specific wind tunnel tests,
wind-induced forces and moments in Main Wind Force
Resisting Systems and Components and Cladding of
selected shapes and sizes of buildings. A public domain set
of such databases, recorded in tests conducted at the
University of Western Ontario (Ho et al. 2005 and St.
Pierre et al. 2005) for buildings with gable roofs is
available on the National Institute of Standards and
Technology (NIST) website: www.nist.gov/wind.
Interpolation software for buildings with similar shape and
with dimensions close to and intermediate between those
included in the set of databases is also available on that
site. Because the database results are for generic
surroundings as permitted in item 3 of Section 207 F. 2 ,
interpolation or extrapolation from these databases should
be used only if condition 2 of Section 207B.1.2 is true.
Extrapolations from available building shapes and sizes
are not permitted, and interpolations in some instances
may not be advisable. For these reasons, the guidance of
an engineer experienced in wind loads on buildings and
familiar with the usage of these databases is recommended.
All databases must have been obtained using testing
methodology that meets the requirements for wind tunnel
testing specified in Section 207F.

207F.4.3 Limitations on Loads

Loads for the main wind force resisting system determined
by wind tunnel testing shall be limited such that the overall
principal loads in the x and y directions are not less than 80
percent of those that would be obtained from Part 1 of
Section 207B or Part 1 of Section 207C. The overall
principal load shall be based on the overturning moment
for flexible buildings and the base shear for other buildings.

Pressures for components and cladding determined by
wind tunnel testing shall be limited to not less than 80
percent of those calculated for Zone 4 for walls and Zone
1 for roofs using the procedure of Section 207E. These
Zones refer to those shown in Figures 207E.4-1, 207E.4-
2A, 207E.4-2B, 207E.4-2C, 207E.4-3, 207E.4-4, 207E.4-
5 A, 207E.4-5B, 207E.4-6, 207E.4-7, and 207E.6-1.

The limiting values of 80 percent may be reduced to 50
percent for the main wind force resisting system and 65
percent for components and cladding if either of the
following conditions applies:

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

2-183

1. There were no specific influential buildings or objects
within the detailed proximity model.

2. Loads and pressures from supplemental tests for all
significant wind directions in which specific
influential buildings or objects are replaced by the
roughness representative of the adjacent roughness
condition, but not rougher than exposure B, are
included in the test results.

207F.5 Wind-Borne Debris

Glazing in buildings in wind-borne debris regions shall be

protected in accordance with Section 207A.10.3.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2- 184 CHAPTER 2 Minimum Design Loads

SECTION 208
EARTHQUAKE LOADS

208.1 General

208.1.1 Purpose

The purpose of the succeeding earthquake provisions is
primarily to design seismic-resistant structures to
safeguard against major structural damage that may lead to
loss of life and property. These provisions are not intended
to assure zero-damage to structures nor maintain their
functionality after a severe earthquake.

208.1.2 Minimum Seismic Design

Structures and portions thereof shall, as a minimum, be
designed and constructed to resist the effects of seismic
ground motions as provided in this section.

208.1.3 Seismic and Wind Design

When the code-prescribed wind design produces greater
effects, the wind design shall govern, but detailing
requirements and limitations prescribed in this section and
referenced sections shall be made to govern.

208.2 Definitions

See Section 202.

208.3 Symbols and Notations

A b = ground floor area of structure to include area
covered by all overhangs and projections, m 2
A c = the combined effective area of the shear walls in
the first storey of the structure, m 2
A e = the minimum cross-sectional area in any
horizontal plane in the first storey of a shear wall,
m 2

A x = the torsional amplification factor at Level x
a p = numerical coefficient specified in Section 208.7
and set forth in Table 208-13
C a = seismic coefficient, as set forth in Table 208-7
C t = numerical coefficient given in Section 208.5.2.2
C v = seismic coefficient, as set forth in Table 208-8
D = dead load

D e = the length of a shear wall in the first storey in the
direction parallel to the applied forces, m
E,E h ,E m ,E v = earthquake loads set forth in Section
208.6

F x = design seismic force applied to Level i, n or x ,
respectively

F p = design seismic force on a part of the structure
F px = design seismic force on a diaphragm

F t = that portion of the base shear, V, considered
concentrated at the top of the structure in addition
to F n

lateral force at Level i for use in Equation 208-

/i “ 14

g = acceleration due to gravity = 9.815 m/sec 2

h if h n , h x = height above the base to Level i, n or x ,
respectively, m

/ = importance factor given in Table 208-1

I p = importance factor for nonstructural component as
given in Table 208-1
L = live load

Level i = level of the structure referred to by the
subscript i

“i = 1” designates the first level above the base
Level n = that level that is uppermost in the main
portion of the structure

Level x = that level that is under design consideration
“x = 1” designates the first level above the base
M = maximum moment magnitude
N a = near-source factor used in the determination of C a
in Seismic Zone 4 related to both the proximity of
the building or structure to known faults with
magnitudes as set forth in Tables 208-4 and 208-5
N v = near-source factor used in the determination of C v
in Seismic Zone 4 related to both the proximity of
the building or structure to known faults with
magnitudes as set forth in Tables 208-4 and 208-6
PI = plasticity index of soil determined in accordance
with approved national standards
R = numerical coefficient representative of the inherent
over-strength and global ductility capacity of
lateral-force-resisting systems, as set forth in Table
208-11 or 208-12

r = a ratio used in determining pDDthe
redundancy/reliability factor. See Section 208.5.
Sa>Sb’S c ,S d ,S e ,S f = soil profile types as set forth

in Table 208-2

T = elastic fundamental period of vibration of the
structure in the direction under consideration,
sec

V = base shear given by Equations. 208-8, 208-9,
208-10, 208-11 or 208-15
V x - the design storey shear in Storey x

W — the total seismic dead load defined in Section

208.5.2.1

w l> w x = that portion of W located at or assigned to
Level i or x, respectively
W v ~ the weight of an element or component
w px = the weight of the diaphragm and the element
tributary thereto at Level x , including applicable
portions of other loads defined in Section

208.6.1

Z — seismic zone factor as given in Table 208-3

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CHAPTER 2 Minimum Design Loads 2 185

A M Maximum Inelastic Response Displacement,

which is the total drift or total storey drift that
occurs when the structure is subjected to the
Design Basis Ground Motion, including
estimated elastic and inelastic contributions to
the total deformation defined in Section
208.6.4.2, mm

A s Design Level Response Displacement, which is

the total drift or total storey drift that occurs
when the structure is subjected to the design
seismic forces, mm

Si horizontal displacement at Level i relative to the

base due to applied lateral forces, f h for use in
Equation 208-14, mm

p Redundancy/Reliability Factor given by

Equation 208-20

ft 0 Seismic Force Amplification Factor, which is

required to account for structural over-strength
and set forth in Table 208-1 1

208.4 Basis for Design

208.4.1 General

The procedures and the limitations for the design of
structures shall be determined considering seismic zoning,
site characteristics, occupancy, configuration, structural
system and height in accordance with this section.
Structures shall be designed with adequate strength to
withstand the lateral displacements induced by the Design
Basis Ground Motion, considering the inelastic response of
the structure and the inherent redundancy, over-strength
and ductility of the lateral force-resisting system.

The minimum design strength shall be based on the Design
Seismic Forces determined in accordance with the static
lateral force procedure of Section 208.5, except as
modified by Section 208.5.3.5.4.

Where strength design is used, the load combinations of
Section 203.3 shall apply. Where Allowable Stress Design
is used, the load combinations of Section 203.4 shall apply.

Allowable Stress Design may be used to evaluate sliding
or overturning at the soil-structure interface regardless of
the design approach used in the design of the structure,
provided load combinations of Section 203.4 are utilized.

208.4.2 Occupancy Categories

For purposes of earthquake-resistant design, each structure
shall be placed in one of the occupancy categories listed in
Table 103-1. Table 208-1 assigns importance factors, / and
/ p , and structural observation requirements for each
category.

Table 208-1 - Seismic Importance Factors

Occupancy
Category 1

Seismic
Importance
Factor, I

Seismic
Importance 2
Factor, I p

I. Essential
Facilities 3

1.50

II. Hazardous
Facilities

1.25

1.50

III. Special

Occupancy

Structures

1.00

IV, Standard
Occupancy
Structures

1.00

V. Miscellaneous
structures

1.00

1 See Table 103-1 for occupancy category listing

2 The limitation of I p for panel connections in Section
208. 7.2.3 shall be 1.0 for the entire connector

3 Structural observation requirements are given in Section
107.9

4 For anchorage of machinery and equipment required for
life-safety systems, the value of I p shall be taken as 1.5

208.4.3 Site Geology and Soil Characteristics

Each site shall be assigned a soil profile type based on
properly substantiated geotechnical data using the site
categorization procedure set forth in Section 208.4.3.1.1
and Table 208-2.

Exception:

When the soil properties are not known in sufficient detail
to determine the soil profile type, Type S D shall be used.
Soil Profile Type S E or S F need not be assumed unless the
building official determines that Type S E or S F may be
present at the site or in the event that Type S E or S F is
established by geotechnical data.

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2-186 CHAPTER 2 - Minimum Design Loads

208.4.3.1 Soil Profile Type

Soil Profile Types S A , S B , S c , S D and are defined in

Table 208-2 and Soil Profile Type S F is defined as soils

requiring site-specific evaluation as follows:

1. Soils vulnerable to potential failure or collapse under
seismic loading, such as liquefiable soils, quick and
highly sensitive clays, and collapsible weakly
cemented soils.

2. Peats and/or highly organic clays, where the thickness
of peat or highly organic clay exceeds 3.0 m.

3 . Very high plasticity clays with a plasticity index, PI >
75, where the depth of clay exceeds 7.5 m.

5. The criteria set forth in the definition for Soil Profile
Type S F requiring site-specific evaluation shall be
considered. If the site corresponds to these criteria, the
site shall be classified as Soil Profile Type S F and a
site-specific evaluation shall be conducted.

208.4.3.1.1 Site Categorization Procedure

208.4.3.1.1.1 Scope

This section describes the procedure for determining Soil

Profile Types S A through S F as defined in Table 208-2.

Very thick soft/medium stiff clays, where the depth of
clay exceeds 35 m.

Table 208-2 - Soil Profile Types

Soil Profile
Type

Soil Profile Name / Generic
Description

Average Soil Properties for Top 30 m of Soil Profile

Shear Wave Velocity,

V s (m/s)

SPT, N( blows/
300 mm)

Undrained

Shear

Strength, S v
(kPa)

Hard Rock

> 1500

S b

Rock

760 to 1500

Very Dense Soil and Soft Rock

360 to 760

>50

> 100

Stiff Soil Profile

180 to 360

15 to 50

50 to 100

Sb 1

Soft Soil Profile

< 180

< 15

<50

S F

Soil Requiring Site-specific Evaluation.

See Section 208.4.3.1

1 Soil Profile Type S E also includes any soil profile with more than 3.0 m of soft clay defined as a soil with plasticity index ,
PI > 20 , w mc > 40% and s u < 24 kPa. The Plasticity Index , PI, and the moisture content , w mc , shall be determined
in accordance with approved national standards.

208.4.3.1.1.2 Definitions

Soil profile types are defined as follows:

S A Hard rock with measured shear wave velocity,

v s > 1500 m/s

S B Rock with 760 m/s < v s < 1500 m/s

S c Very dense soil and soft rock with 360 m/s <

v s < 760 m/s or with either N > 50 or s u >

100 kPa

S D Stiff soil with 180 m/s <vs< 360 m/s or

with 15 < IV < 50 or 50 kPa < s u <

100 kPa

S E A soil profile with v s < 180 m/s or any
profile with more than 3 m of soft clay defined
as soil with PI > 20, w mc > 40 percent and

s u < 25 kPa

S F Soils requiring site-specific evaluation, refer to
Section 208.4.3.1

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CHAPTER 2 — Minimum Design Loads 2-187

208.4.3.1.1.2.1 v s , Average Shear Wave Velocity

v s shall be determined in accordance with the following
equation:

s v „ dj_ (208-1)

Li= 1 v sl

where

di = thickness of Layer i , m

v si = shear wave velocity in Layer i , m/s

208.4.3.1.1.2.2 Af, Average Field
Standard Penetration Resistance and
N ch , Average Standard Penetration
Resistance for Cohesionless Soil
Layers

N and N cfl shall be determined in accordance with the
following equation:

N =^i±

" yn di (208-2)

^i=i N .

Nch (208-3)

U=t N.

where

d t = thickness of Layer i in mm

d s = the total thickness of cohesionless soil layers
in the top 30 m

N t = the standard penetration resistance of soil
layer in accordance with approved nationally
recognized standards

208.4.3.1.1.2.3 s u , Average Undrained Shear
Strength

s u shall be determined in accordance with the following
equation:

208.4.3.1.1.2.4 Rock Profiles, S A and S B

The shear wave velocity for rock, Soil Profile Type S B ,
shall be either measured on site or estimated by a
geotechnical engineer, engineering geologist or
seismologist for competent rock with moderate fracturing
and weathering. Softer and more highly fractured and
weathered rock shall either be measured on site for shear
wave velocity or classified as Soil Profile Type S c .

The hard rock, Soil Profile Type S A , category shall be
supported by shear wave velocity measurement either on
site or on profiles of the same rock type in the same
formation with an equal or greater degree of weathering
and fracturing. Where hard rock conditions are known to
be continuous to a depth of 30 m, surficial shear wave
velocity measurements may be extrapolated to assess v s .
The rock categories, Soil Profile Types S A and S B , shall
not be used if there is more than 3 meters of soil between
the rock surface and the bottom of the spread footing or mat
foundation.

The definitions presented herein shall apply to the upper
30 m of the site profile. Profiles containing distinctly
different soil layers shall be subdivided into those layers
designated by a number from 1 to n at the bottom, where
there are a total of n distinct layers in the upper 30 m. The
symbol i then refer to any one of the layers between 1 and
n.

208.4.3.1.1.2.5 Soft Clay Profile, S E

The existence of a total thickness of soft clay greater than
3 m shall be investigated where a soft clay layer is defined
by s u < 24 kPa, w mc > 40 percent and PI > 20. If
these criteria are met, the site shall be classified as Soil
Profile Type S E .

208.4.3.1.1.2.6 Soil Profiles S c , S D and S E

Sites with Soil Profile Types S c , S D and S E shall be
classified by using one of the following three methods with
v s , N and s u computed in all cases as specified in Section
208.4.3.1.1.2.

where

“ v „ A (2°8- 4 )

the total thickness (100 — d s ) of cohesive
soil layers in the top 30 m
the undrained shear strength in accordance
with approved nationally recognized
standards, not to exceed 250 kPa

National Structural Code of the Philippii

1. v s for the top 30 meters (v s method).

2. N for the top 30 meters (N method).

3. N ch for cohesionless soil layers {PI < 20) in the top
30 m and average s u for cohesive soil layers {PI >
20) in the top 30 m (s u method).

ies Volume I, 7th Edition, 2015

2-188 CHAPTER 2 - Minimum Design Loads

208.4.4 Site Seismic Hazard Characteristics

Seismic hazard characteristics for the site shall be
established based on the seismic zone and proximity of the
site to active seismic sources, site soil profile
characteristics and the structure's importance factor.

208.4.4.1 Seismic Zone

The Philippine archipelago is divided into two seismic
zones only. Zone 2 covers the provinces of Palawan
(except Busuanga) , Sulu and Tawi-Tawi while the rest of
the country is under Zone 4 as shown in Figure 208-1. Each
structure shall be assigned a seismic zone factor Z, in
accordance with Table 208-3.

Table 208-3 Seismic Zone Factor Z

ZONE

0.20

0.40

208.4.4.2 Seismic Source Types

Table 208-4 defines the types of seismic sources. The
location and type of seismic sources to be used for design
shall be established based on approved geological data; see
Figure 208-2A. Type A sources shall be determined from
Figure 208-2B, 2C, 2D, 2E or the most recent mapping of
active faults by the Philippine Institute of Volcanology and
Seismology (PHIVOLCS).

Table 208-4 - Seismic Source Types 1

Seismic

Source

Type

Seismic Source
Description

Seismic Source
Definition

Maximum Moment
Magnitude, M

Faults that are
capable of
producing large
magnitude events
and that have a
high rate of seismic
activity.

7.0 < M < 8.4

All faults other
than Types A and

6.5 < M < 7.0

Faults that are not
capable of
producing large
magnitude
earthquakes and
that have a
relatively low rate
of seismic activity.

M < 6.5

*S ubduction sources shall be evaluated on a site-
specific basis.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads

Figure 208-1 Referenced Seismic Map of the Philippines
National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-190 CHAPTER 2 - Minimum Design Loads

Distribution of Active Faults and Trenches
in the Philippines

Figure 208-2A Distribution of Active Faults and Trenches in the Philippines
Association of Structural Engineers of the Philippines, Inc, (ASEP)

CHAP! ER 2 — Minimum Design Loads

2401

Distribution of Active Faults in
Cordillera Administrative Region (CAR)

Earthquake Sourest
Active Faults
— — JUMMw.eaottttwWn

Dashed hoe - trace is approximate
Approxrmala oflahore projection

• Capital City /Municipality

0 IQ 20 JO 40 SO

Figure 208-2B Distribution of Active Faults in Cordillera Administrative Region (CAR)
National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-192 CHAPTER 2 - Minimum Design Loads

Distribution of Active Faults and Trenches

in Region 1

Earthquake Sources
Active Faults

tx*l f kp« rn (■!*■»

OMhad IM - boo* I* ^nninM

Converg en ce Zone

****** TfwnJi

Figure 208-2C Distribution of Active Faults and Trenches in Region 1
Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-193

Distribution of Active Faults and Trenches

in Region 2

Figure 208-2D Distribution of Active Faults and Trenches in Region 2
National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-194 CHAPTER 2 - Minimum Design Loads

Association of Structural Engineers of the Philippines, Inc. (ASEP)

Distribution of Active Faults
Region 3

Figure 208-2F Distribution of Active Faults and Trenches in Region 4A

National Structural Code of the Philippines Volume l, 7th Edition, 2015

2-196 CHAPTER 2 - Minimum Design Loads

Association of Structural Engineers of the Philippines, Inc. (ASEP)

Distribution of Active Faults and Trenches
in Region 4B

Figure 208-2E Distribution of Active Faults in Region 5
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2-138 CHAPTER 2 - Minimum Design Loads

Distribution of Active Faults and Trenches in Region 6

Association of Structural Engineers of the Philippines, Inc, (ASEP)

CHAPTER 2- Minimum Design Loads

2-199

Distribution of Active Faults in Region 7

Figure 208-2G Distribution of Active Faults in Region 7

National Structural Code of the Philippines Volume I, 7th Edition, 2015

-200 CHAPTER 2 - Minimum Design l oads

NORTHERN SAMAR

Distribution of Active Faults in Region 8

Earthquake Sources
Active Faults

Betid £r* ■ V9i*> it MfUWf
- - - Dashed lira - (race Is approximate
Approximate offshore projection

Capital City /Municipality

Figure 208-2H Distribution of Active Faults in Region 8

Association of Structural Engineers of the Philippines, Inc, (ASEP)

Distribution of Active Faults and Trenches in
Autonomous Region of Muslim Mindanao (ARMM)

CHAPTER 2 - Minimum Design Loads 2-201

Figure 208-21 Distribution of Active Faults and Trenches in Autonomous Region of Muslim Mindanao (ARMM)

National Structural Code of the Philippines Volume I, 7th Edition. 2015

2*202 CHAPTER Z— Minimum Design Loads

Distribution of Active Faults and Trenches in Region 9

Figure 208-2J Distribution of Active Faults and Trenches in Region 9

Association of Structural Engineers of the Philippines. Inc. (ASEP)

Figure 208-2K Distribution of Active Faults and Trenches in Region 10

2-203

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-204 CHAPTER 2 - Minimum Design Loads

Distribution of Active Faults and Trenches

in Region 11

Figure 208-2L Distribution of Active Faults in Region 1 1

Association of Structural Engineers of the Philippines, Inc. (ASEP)

C H A P T E R 2 - Minii li u m D m i g « L o ads

2-205

Distribution of Active Faults and Trenches

Figure 208-2M Distribution of Active Faults and Trenches in Region 12
National Structural Code of the Philippines Volume I. 7th Edition. 2015

2-206 CHAPTER 2 - Minimum Design Loads

Distribution of Active Faults and Trenches

in Region 13

Figure 208-2N Distribution of Active Faults and Trenches in Region 13

Association of Structural Engineers of the Philippines. Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-207

208.4.4.3 Seismic Zone 4 Near-Source Factor

Jn Seismic Zone 4, each site shall be assigned near-source
factors in accordance with Tables 208-5 and 208-6 based
on the Seismic Source Type as set forth in Section
208.4.4.2.

4. The exceptions to Section 515.6.5 shall not apply,
except for columns in one-storey buildings or columns
at the top storey of multistorey buildings.

5. None of the following structural irregularities is
present: Type 1, 4 or 5 of Table 208-9, and Type l or
4 of Table 208-10.

For high rise structures and essential facilities within
2.0 km of a major fault, a site specific seismic elastic design
response spectrum is recommended to be obtained for the
specific area.

Table 208-5 Near-Source Factor N a 1

Seismic

Closest Distance To

Source

Known Seismic Source 2

T y.P e

<2 km

< 5 km

> 10 km

1.5

1.2

1.0

1.3

1.0

Table 208-6 Near-Source Factor, N v 1

Seismic

Source

Type

Closest Distance To

Known Seismic Source 2

<2 km

5 km

10 km

> 15 km

2.0

1.6

1.2

1.0

1.6

1.2

1.0

Notes for Tables 208.5 and 208.6:

1 The Near-Source Factor may be based on the linear
interpolation of values for distances other than those
shown in the table.

2 The closest distance to seismic source shall be taken
as the minimum distance between the site and the area
described by the vertical projection of the source on
the surface (i.e., surface projection of fault plane). The
surface projection need not include portions of the
source at depths of 10 km or greater. The largest value
of the Near-Source Factor considering all sources
shall be used for design.

The value of N a used to determine C a need not exceed 1 . 1

for structures complying with all the following conditions:

208.4.4,4 Seismic Response Coefficients

Each structure shall be assigned a seismic coefficient, C a ,
in accordance with Table 208-7 and a seismic coefficient,
C v , in accordance with Table 208-8.

Table 208-7 Seismic Coefficient, C a

Soil Profile
Type

Seismic Zone Z

Z = 0.2

Z = 0.4

S A

0.16

0.32 N a

0.20

0A0N n

0.24

0A0N a

S D

0.28

0A4N a

0.34

0A4N a

See Footnote 1 of Table 208-8

Table 208-8 Seismic Coefficient, C v

Soil Profile
Type

Seismic Zone Z

Z = 0.2

Z = 0.4

S A

0.16

0.32AV

0.20

OAONv

0.32

0.56AV

0.40

0.64AT

Sjj

0.64

0.96AV

See Footnote 1 of Table 208-8

! Site-specific geotechnical investigation and dynamic site
response analysis shall be performed to determine
seismic coefficients

208.4.5 Configuration Requirements

Each structure shall be designated as being structurally
regular or irregular in accordance with Sections 208.4.5.1
and 208.4.5.2.

1 . The soil profile type is S A , S B , S c or S D .

2 . p= 1 . 0 .

3. Except in single-storey structures, residential building
accommodating 10 or fewer persons, private garages,
carports, sheds and agricultural buildings, moment
frame systems designated as part of the lateral-force-
resisting system shall be special moment-resisting
frames.

208.4.5.1 Regular Structures

Regular structures have no significant physical
discontinuities in plan or vertical configuration or in their
lateral-force-resisting systems such as the irregular features
described in Section 208.4.5.2.

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2-208 CHAPTER 2 - Minimum Design Loads

208.4.5.2 Irregular Structures

1. Irregular structures have significant physical
discontinuities in configuration or in their lateral-
force-resisting systems. Irregular features include, but
are not limited to, those described in Tables 208-9 and
208-10. All structures in occupancy Categories 4 and
5 in Seismic Zone 2 need to be evaluated only for
vertical irregularities of Type 5 (Table 208-9) and
horizontal irregularities of Type 1 (Table 208-10).

2. Structures having any of the features listed in Table
208-9 shall be designated as if having a vertical
irregularity.

Exception:

Where no storey drift ratio under design lateral forces is
greater them 1.3 times the storey drift ratio of the storey
above, the structure may be deemed to not have the
structural irregularities of Type / or 2 in Table 208-9. The
store}’ drift ratio for the top two stories need not he
considered. The storey drifts for this determination may be
calculated neglecting torsional effects.

3. Structures having any of the features listed in Table
208-10 shall be designated as having a plan
irregularity.

Table 208-9 Vertical Structural Irregularities

Irregularity Type and Definition

Reference

Section

1. Stiffness Irregularity - Soft
Storey

A soft storey is one in which the
lateral stiffness is less than 70 % of
that in the storey above or less than
80 percent of the average stiffness
of the three stories above.

208.4.8.3

Item 2

2. Weight (Mass) Irregularity

Mass irregularity shall be

considered to exist where the
effective mass of any storey is more
than 150 % of the effective mass of
an adjacent storey. A roof that is
lighter than the floor below need
not be considered.

208.4.8.3

Item 2

3. Vertical Geometric Irregularity

Vertical geometric irregularity shall
be considered to exist where the
horizontal dimension of the lateral-
force-resisting system in any storey
is more than 130 % of that in an
adjacent storey. One-storey

penthouses need not be considered.

208.4.8.3
Item 2

4. In-Plane Discontinuity In

Vertical Lateral-Force-Resisting
Element Irregularity

An in-plane offset of the lateral-
load-resisting elements greater than
the length of those elements.

208.5.8.1.5.

5. Discontinuity In Capacity -
Weak Storey Irregularity

A weak storey is one in which the
storey strength is less than 80 % of
that in the storey above. The storey
strength is the total strength of all
seismic-resisting elements sharing
the storey for the direction under
consideration.

208.4.9.1

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CHAPTER 2 - Minimum Design Loads 2-209

Table 208-10 Horizontal Structural Irregularities

Irregularity Type and Definition

Reference

Section

1. Torsional Irregularity - To Be

Considered When Diaphragms Are
Not Flexible

Torsional irregularity shall be
considered to exist when the
maximum storey drift, computed
including accidental torsion, at one
end of the structure transverse to an
axis is more than 1.2 times the
average of the storey drifts of the two
ends of the structure.

208.7.2.7
Item 6

2. Re-Entrant Corner Irregularity

Plan configurations of a structure and
its lateral-force-resisting system
contain re-entrant corners, where both
projections of the structure beyond a
re-entrant corner are greater than 1 5
% of the plan dimension of the
structure in the given direction.

208.7.2.7
Items 6
and 7

3. Diaphragm Discontinuity
Irregularity

Diaphragms with abrupt

discontinuities or variations in
stiffness, including those having
cutout or open areas greater than 50 %
of the gross enclosed area of the
diaphragm, or changes in effective
diaphragm stiffness of more than 50
% from one storey to the next.

208.7.2.7
Item 6

4. Out-Of-Plane Offsets Irregularity

Discontinuities in a lateral force path,
such as out-of-plane offsets of the
vertical elements

208.5.8.5.

208.7.2.7
Item 6;

5. Non-parallel Systems Irregularity

The vertical lateral-load-resisting
elements are not parallel to or
symmetric about the major orthogonal
axes of the lateral force-resisting
systems.

208.7.1

208.4.6 Structural Systems

Structural systems shall be classified as one of the types
listed in Table 208-1 1 and defined in this section.

208.4.6.1 Bearing Wall System

A structural system without a complete vertical load-
carrying space frame. Bearing walls or bracing systems
provide support for all or most gravity loads. Resistance to
lateral load is provided by shear walls or braced frames.

208.4.6.2 Building Frame System

A structural system with an essentially complete space
frame providing support for gravity loads. Resistance to
lateral load is provided by shear walls or braced frames.

208.4.6.3 Moment-Resisting Frame System

A structural system with an essentially complete space
frame providing support for gravity loads. Moment-
resisting frames provide resistance to lateral load primarily
by flexural action of members.

208.4.6.4 Dual System

A structural system with the following features:

1. An essentially complete space frame that provides
support for gravity loads.

2. Resistance to lateral load is provided by shear walls or
braced frames and moment-resisting frames (SMRF,
IMRF, MMRWF or steel OMRF). The moment-
resisting frames shall be designed to independently
resist at least 25 percent of the design base shear.

3. The two systems shall be designed to resist the total
design base shear in proportion to their relative
rigidities considering the interaction of the dual system
at all levels.

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208.4.6.5 Cantilevered Column System

A structural system relying on cantilevered column
elements for lateral resistance.

208.4.6.6 Undefined Structural System
A structural system not listed in Table 208-1 1 .

208.4.6.7 Non-building Structural System
A structural system conforming to Section 208.8.

208.4.7 Height Limits

Height limits for the various structural systems in Seismic
Zone 4 are given in Table 208-1 1 .

Exception:

Regular structures may exceed these limits by not more
than 50 percent for unoccupied structures, which are not
accessible to the general public.

208.4.8 Selection of Lateral Force Procedure

Any structure may be, and certain structures defined below
shall be, designed using the dynamic lateral-force
procedures of Section 208.5.3.

208.4.8.1 Simplified Static

The simplified static lateral-force procedure set forth in
Section 208.5. 1 . 1 may be used for the following structures
of Occupancy Category IV or V:

1 . Buildings of any occupancy (including single-family
dwellings) not more than three stories in height
excluding basements that use light-frame construction.

2. Other buildings not more than two stories in height
excluding basements.

208.4.8.2 Static

The static lateral force procedure of Section 208.5 may be
used for the following structures:

1. All structures, regular or irregular in Occupancy
Categories IV and V in Seismic Zone 2.

2. Regular structures under 75 m in height with lateral
force resistance provided by systems listed in Table
208-11, except where Section 208.4.8.3, Item 4,
applies.

3. Irregular structures npt more than five stories or 20 m
in height.

4. Structures having a llexible upper portion supported
on a rigid lower portion where both portions of the
structure considered separately can be classified as
being regular, the average storey stiffness of the lower
portion is at least 10 times the average storey stiffness
of the upper portion and the period of the entire
structure is not greater than 1.1 times the period of the
upper portion considered as a separate structure fixed
at the base.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-21 1

208.4.8.3 Dynamic

The dynamic lateral-force procedure of Section 208.5.3
shall be used for all other structures, including the
following:

1 . Structures 75 m or more in height, except as permitted
by Section 208.4.8,2, Item 1.

2. Structures having a stiffness, weight or geometric
vertical irregularity of Type 1, 2 or 3, as defined in
Table 208-9, or structures having irregular features not
described in Table 208-9 or 208-10, except as
permitted by Section 208.4.10.3.1.

3. Structures over five stories or 20 m in height in
Seismic Zone 4 not having the same structural system
throughout their height except as permitted by Section
208.5.3.2.

4. Structures, regular or irregular, located on Soil Profile
Type S f , that have a period greater than 0.7 s. The
analysis shall include the effects of the soils at the site
and shall conform to Section 208.5.3.2, Item 4.

208.4.8.4 Alternative Procedures

208.4.8.4.1 General

Alternative lateral-force procedures using rational analyses
based on well-established principles of mechanics may be
used in lieu of those prescribed in these provisions.

208.4.8.4.2 Seismic Isolation

Seismic isolation, energy dissipation and damping systems
may be used in the analysis and design of structures when
approved by the building official and when special
detailing is used to provide results equivalent to those
obtained by the use of conventional structural systems.

208.4.9 System Limitations

208.4.9.1 Discontinuity

Structures with a discontinuity in capacity, vertical
irregularity Type 5 as defined in Table 208-9, shall not be
over two stories or 9 m in height where the weak storey has
a calculated strength of less than 65 % of the storey above.

Exception :

Where the weak storey is capable of resisting a total lateral
seismic force of fl 0 times the design force prescribed in
Section 208.5 .

208.4.9.2 Undefined Structural Systems

For undefined structural systems not listed in Table 208-
11, the coefficient R shall be substantiated by approved
cyclic test data and analyses. The following items shall be
addressed when establishing R:

1 . Dynamic response characteristics,

2. Lateral force resistance,

3. Over-strength and strain hardening or softening,

4. Strength and stiffness degradation,

5. Energy dissipation characteristics,

6. System ductility, and

7. Redundancy.

208.4.9.3 Irregular Features

All structures having irregular features described in Table
208-9 or 208-10 shall be designed to meet the additional
requirements of those sections referenced in the tables.

208.4.10 Determination of Seismic Factors

208.4.10.1 Determination offl 0

For specific elements of the structure, as specifically
identified in this code, the minimum design strength shall
be the product of the seismic force over-strength factor H 0
and the design seismic forces set forth in Section 208.5. For
both Allowable Stress Design and Strength Design, the
Seismic Force Over- strength Factor, shall be taken
from Table 208-11.

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208.4.10.2 Determination of R

The value for R shall be taken from Table 208-1 1 .

208.4.10.3 Combinations of Structural Systems

Where combinations of structural systems are incorporated
into the same structure, the requirements of this section
shall be satisfied.

208.4.10.3.1 Vertical Combinations

The value of R used in the design of any storey shall be less
than or equal to the value of R used in the given direction
for the storey above.

Exception:

This requirement need not be applied to a storey where the
deadweight above that storey is less than 10 percent of the
total dead weight of the structure.

Structures may be designed using the procedures of this
section under the following conditions:

The entire structure is designed using the lowest R of the
lateral force-resisting systems used, or

1. The following two-stage static analysis procedures
may be used for structures conforming to Section
208.4.8.2, Item 4.

1 . 1 The flexible upper portion shall be designed as a
separate structure, supported laterally by the rigid
lower portion, using the appropriate values of R
and p.

1.2 The rigid lower portion shall be designed as a
separate structure using the appropriate values of
R and p. The reactions from the upper portion
shall be those determined from the analysis of the
upper portion amplified by the ratio of the ( R / p)
of the upper portion over (R/p) of the lower
portion.

208.4.10.3.2 Combinations along Different Axes

In Seismic Zone 4 where a structure has a bearing wall
system in only one direction, the value of R used for design
in the orthogonal direction shall not be greater than that
used for the bearing wall system.

Any combination of bearing wall systems, building frame
systems, dual systems or moment-resisting frame systems
may be used to resist seismic forces in structures less than
50 m in height. Only combinations of dual systems and
special moment-resisting frames shall be used to resist

seismic forces in structures exceeding 50 m in height in
Seismic Zone 4.

208.4.10.3.3 Combinations along the Same Axis

Where a combination of different structural systems is
utilized to resist lateral forces in the same direction, the
value of R used for design in that direction shall not be
greater than the least value for any of the systems utilized
in that same direction.

208.5 Minimum Design Lateral Forces and Related
Effects

208.5.1 Simplified Static Force Procedure

Structures conforming to the requirements of Section

208.4.8.1 may be designed using this procedure.

208.5.1.1 Simplified Design Base Shear

The total design base shear in a given direction shall be
determined from the following equation:

V = —W (208-5)

where the value of C a shall be based on Table 208-7 for the
soil profile type. When the soil properties are not known
in sufficient detail to determine the soil profile type. Type
S D shall be used in Seismic Zone 4, and Type S E shall be
used in Seismic Zone 2. In Seismic Zone 4, the Near-
Source Factor, N a , need not be greater than 1 .2 if none of
the following structural irregularities are present:

1 . Type 1 , 4 or 5 of Table 208-9, or

2. Type 1 or 4 of Table 208-10.

208.5.1.2 Vertical Distribution

The forces at each level shall be calculated using the
following equation:

F=^ Wl (208-6)

where the value of C a shall be determined as in Section
208.5.1.1.

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208.5.1.3 Horizontal Distribution of Shear

The design storey shear, V x , in any storey is the sum of the
forces F t and F x above that storey. V x shall be distributed
to the various elements of the vertical lateral force-resisting
system in proportion to their rigidities, considering the
rigidity of the diaphragm. See Section 208.7.2.3 for rigid
elements that are not intended to be part of the lateral force-
resisting systems.

where

8 avg = ^e average of the displacements at the
extreme points of the structure at Level x,
mm

8 max = the maximum displacement at Level x ,
mm

The value of A x need not exceed 3.0

Where diaphragms are not flexible, the mass at each level
shall be assumed to be displaced from the calculated center
of mass in each direction a distance equal to 5 percent of
the building dimension at that level perpendicular to the
direction of the force under consideration. The effect of
this displacement on the storey shear distribution shall be
considered.

Diaphragms shall be considered flexible for the purposes
of distribution of storey shear and torsional moment when
the maximum lateral deformation of the diaphragm is more
than two times the average storey drift of the associated
storey. This may be determined by comparing the
computed midpoint in-plane deflection of the diaphragm
itself under lateral load with the storey drift of adjoining
vertical-resisting elements under equivalent tributary
lateral load.

208.5.1.5 Overturning

Every structure shall be designed to resist the overturning
effects caused by earthquake forces specified in Section
208,5.2,3. At any level, the overturning moments to be
resisted shall be determined using those seismic forces ( F t
and F x ) that act on levels above the level under
consideration. At any level, the incremental changes of the
design overturning moment shall be distributed to the
various resisting elements in the manner prescribed in
Section 208.5.1.3. Overturning effects on every element
shall be carried down to the foundation. See Sections 207. 1
and 208.7 for combining gravity and seismic forces.

208.5.1.5.1 Elements Supporting Discontinuous

Systems

208.5.1.5.1.1 General

208.5.1.4 Horizontal Torsional Moments

Provisions shall be made for the increased shears resulting
from horizontal torsion where diaphragms are not flexible.
The most severe load combination for each element shall
be considered for design.

The torsional design moment at a given storey shall be the
moment resulting from eccentricities between applied
design lateral forces at levels above that storey and the
vertical-resisting elements in that storey plus an accidental
torsion.

The accidental torsional moment shall be determined by
assuming the mass is displaced as required by Section
208.5.1.3.

Where any portion of the lateral load-resisting system is
discontinuous, such as for vertical irregularity Type 4 in
Table 208-9 or plan irregularity Type 4 in Table 208-10,
concrete, masonry, steel and wood elements supporting
such discontinuous systems shall have the design strength
to resist the combination loads resulting from the special
seismic load combinations of Section 203.5.

Exceptions:

1. The quantity E m in Section 208.6 need not exceed the
maximum force that can be transferred to the element
by the lateral-force-resisting system.

2. Concrete slabs supporting light-frame wood shear
wall systems or light-frame steel and wood structural
panel shear wall systems .

Where torsional irregularity exists, as defined in Table
208-10, the effects shall be accounted for by increasing the
accidental torsion at each level by an amplification factor,
A x , determined from the following equation:

1 . 26 ,

avf]}

(208-7)

For Allowable Stress Design, the design strength may be
determined using an allowable stress increase of 1 .7 and a
resistance factor, 0, of 1.0. This increase shall not be
combined with the one- third stress increase permitted by
Section 203.4, but may be combined with the duration of
load increase permitted in Section 615.3.4.

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208.5.1.5.1-1-2 Detailing requirements in Seismic
Zone 4

In Seismic Zone 4, elements supporting discontinuous

systems shall meet the following detailing or member

limitations:

1 . Reinforced concrete or reinforced masonry elements
designed primarily as axial-load members shall
comply with Section 421.4.4.5.

2. Reinforced concrete elements designed primarily as
flexural members and supporting other than light-
frame wood shear wall system or light-frame steel and
wood structural panel shear wall systems shall comply
with Sections 421.3.2 and 421.3.3. Strength
computations for portions of slabs designed as
supporting elements shall include only those portions
of the slab that comply with the requirements of these
sections.

3. Masonry elements designed primarily as axial-load
carrying members shall comply with Sections
706.1.12.4, Item 1, and 708.2.6.2.6.

4. Masonry elements designed primarily as flexural
members shall comply with Section 708.2.6.2.5.

5. Steel elements designed primarily as axial-load
members shall comply with Sections 515.4.2 and
515.4.3.

6. Steel elements designed primarily as flexural members
or trusses shall have bracing for both top and bottom
beam flanges or chords at the location of the support
of the discontinuous system and shall comply with the
requirements of Section 515.6.1.3.

7. Wood elements designed primarily as flexural
members shall be provided with lateral bracing or
solid blocking at each end of the element and at the
connection location(s) of the discontinuous system.

208.5.1.6 Applicability

Sections 208.6.2, 208.6.3, 208.5.2.1, 208.5.2.2, 208.5.2.3,
208.6.4,208.6.5 and 208.5.3 shall not apply when using the
simplified procedure.

Exception:

For buildings with relatively flexible structural systems,
the building official may require consideration of PA
effects and drift in accordance with Sections 208.63,
208.6.4 and 208.6.5. A s shall be determined using design
seismic forces from Section 208.5.1.1.

Where used, A M shall be taken equal to 0.01 times the
storey height of all stories. In Section 208.7.2.7,

Equation 208-22 shall read F px = ~^w V x and need not
exceed C a w px , but shall not be less than 0. 5 C a w px . R and
fl 0 shall be taken from Table 208-11.

208.5.2 Static Force Procedure

208.5.2.1 Design Base Shear

The total design base shear in a given direction shall be
determined from the following equation:

v = £lL W (208-8)

The total design base shear need not exceed the following:

2 /

v= a W (208-9)

The total design base shear shall not be less than the
following:

F = 0 .11 C a IW (208-10)

208.5.1.5.2 At Foundation

See Sections 208.4.1 and 308.4 for overturning moments
to be resisted at the foundation soil interface.

In addition, for Seismic Zone 4, the total base shear shall
also not be less than the following:

0. 8 ZNJ

V - —W

(208-11)

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CHAPTER 2 - Minimum Design Loads 2-215

208.5.2.2 Structure Period

The value of T shall be determined from one of the
following methods:

distribution. The elastic deflections, S h shall be calculated
using the applied lateral forces, /*.

208.5.2.3 Vertical Distribution of Force

1. Method A:

For all buildings, the value T may be approximated from
the following equation:

The total force shall be distributed over the height of the
structure in conformance with Equations 208-15, 208-16
and 208-17 in the absence of a more rigorous procedure.

T = C t (h n ) 3/ * (208-12)

where

V = F t +^F t

i = 1

(208-15)

C t = 0.0853 for steel moment-resisting frames

C t = 0.0731 for reinforced concrete moment-

resisting frames and eccentrically braced
frames

C t = 0.0488 for all other buildings

The concentrated force F t at the top, which is in addition
to F n , shall be determined from the equation:

F t = 0.077V (208-16)

Alternatively, the value of C t for structures with concrete
or masonry shear walls may be taken as 0.0743/V^:

The value of A c shall be determined from the following
equation:

A c = ^A e [0.2 + (D e /h n ) 2 ] (208-13)

The value of D e /h n used in Equation 208-13 shall not
exceed 0.9.

2. Method B:

The fundamental period T may be calculated using the
structural properties and deformational characteristics of
the resisting elements in a properly substantiated analysis.
The analysis shall be in accordance with the requirements
of Section 208.6.2. The value of T from Method B shall
not exceed a value 30 percent greater than the value of T
obtained from Method A in Seismic Zone 4, and 40 percent
in Seismic Zone 2.

The value of T used for the purpose of calculating F t shall
be the period that corresponds with the design base shear
as computed using Equation 208-4. F t need not exceed
0. 25F and may be considered as zero where T is 0.7 s or
less. The remaining portion of the base shear shall be
distributed over the height of the structure, including Level
n, according to the following equation:

(V~F t )w x h x

w t h,

(208-17)

At each level designated as x , the force F x shall be applied
over the area of the building in accordance with the mass
distribution at that level. Structural displacements and
design seismic forces shall be calculated as the effect of
forces F x and F t applied at the appropriate levels above the
base.

208.5.3 Dynamic Analysis Procedures
208.5.3.1 General

The fundamental period T may be computed by using the
following equation:

T =

. I (ZUwfi)

(208-14)

Dynamic analyses procedures, when used, shall conform to
the criteria established in this section. The analysis shall be
based on an appropriate ground motion representation and
shall be performed using accepted principles of dynamics.

Structures that are designed in accordance with this section
shall comply with all other applicable requirements of
these provisions.

The values of f t represent any lateral force distributed
approximately in accordance with the principles of
Equations. 208-15, 208-16 and 208- 17 or any other rational

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208.5.3.2 Ground Motion

T£e ground motion representation shall, as a minimum, be
one having a 10-percent probability of being exceeded in
50 years, shall not be reduced by the quantity R and may
be one of the following:

h An elastic design response spectrum constructed in
accordance with Figure 208-3, using the values of C a
and C v consistent with the specific site. The design
acceleration ordinates shall be multiplied by the
acceleration of gravity, 9.815 m/sec 2 .

2. A site-specific elastic design response spectrum based
on the geologic, tectonic, seismologic and soil
characteristics associated with the specific site. The
spectrum shall be developed for a damping ratio of
0.05, unless a different value is shown to be consistent
with the anticipated structural behavior at the intensity
of shaking established for the site.

3. Ground motion time histories developed for the
specific site shall be representative of actual
earthquake motions. Response spectra from time
histories, either individually or in combination, shall
approximate the site design spectrum conforming to
Section 208.5.3.2, Item 2,

4. For structures on Soil Profile Type S F , the following
requirements shall apply when required by Section
208.4.8.3, Item 4:

4. 1 The ground motion representation shall be
developed in accordance with Items 2 and 3.

4.2 Possible amplification of building response due to
the effects of soil-structure interaction and
lengthening of building period caused by inelastic
behavior shall be considered.

5. The vertical component of ground motion may be
defined by scaling corresponding horizontal
accelerations by a factor of two- thirds. Alternative
factors may be used when substantiated by site-
specific data. Where the Near-Source Factor, N a , is
greater than 1 . 0 , site-specific vertical response spectra
shall be used in lieu of the factor of two-thirds.

Figure 208-3
Design Response Spectra

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 Minimum Dfllign Loads

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208.5.3.3 Mathematical Model

A mathematical model of the physical structure shall
represent the spatial distribution of the mass and stiffness
of the structure to an extent that is adequate for the
calculation of the significant features of its dynamic
response. A three-dimensional model shall be used for the
dynamic analysis of structures with highly irregular plan
configurations such as those having a plan irregularity
defined in Table 208-10 and having a rigid or semi-rigid
diaphragm. The stiffness properties used in the analysis
and general mathematical modeling shall be in accordance
with Section 208.6.2.

208.5.3.4 Description of Analysis Procedures

208.5.3.4.1 Response Spectrum Analysis

An elastic dynamic analysis of a structure utilizing the peak
dynamic response of all modes having a significant
contribution to total structural response. Peak modal

responses are calculated using the ordinates of the
appropriate response spectrum curve which correspond to
the modal periods. Maximum modal contributions are
combined in a statistical manner to obtain an approximate
total structural response.

208.5.3.4.2 Time History Analysis

An analysis of the dynamic response of a structure at each
increment of time when the base is subjected to a specific
ground motion time history.

208.5.3.5 Response Spectrum Analysis

208.5.3.5.1 Response Spectrum Representation
and Interpretation of Results

The ground motion representation shall be in accordance
with Section 208.5.3.2. The corresponding response
parameters, including forces, moments and displacements,
shall be denoted as Elastic Response Parameters. Elastic
Response Parameters may be reduced in accordance with
Section 208.5.3.5.4.

The base shear for a given direction, determined using
dynamic analysis must not be less than the value obtained
by the equivalent lateral force method of Section 208.5.2.
In this case, all corresponding response parameters are
adjusted proportionately.

208.5.3.5.2 Number of Modes

The requirement of Section 208.5.3.4.1 that all significant
modes be included may be satisfied by demonstrating that

for the modes considered, at least 90 percent of the
participating mass of the structure is included in the
calculation of response for each principal horizontal
direction.

208.5.3.5.3 Combining Modes

The peak member forces, displacements, storey forces,
storey shears and base reactions for each mode shall be
combined by recognized methods. When three-
dimensional models are used for analysis, modal
interaction effects shall be considered when combining
modal maxima.

208.5.3.5.4 Reduction of Elastic Response
Parameters for Design

Elastic Response Parameters may be reduced for purposes
of design in accordance with the following items, with the
limitation that in no case shall the Elastic Response
Parameters be reduced such that the corresponding design
base shear is less than the Elastic Response Base Shear
divided by the value of R.

1 . For all regular structures where the ground motion
representation complies with Section 208.5.3.2, Item

1, Elastic Response Parameters may be reduced such
that the corresponding design base shear is not less
than 90 percent of the base shear determined in
accordance with Section 208.5.2.

2. For all regular structures where the ground motion
representation complies with Section 208.5.3.2, Item

2, Elastic Response Parameters may be reduced such
that the corresponding design base shear is not less
than 80 percent of the base shear determined in
accordance with Section 208.5.2,

3. For all irregular structures, regardless of the ground
motion representation, Elastic Response Parameters
may be reduced such that the corresponding design
base shear is not less than 1 00 percent of the base shear
determined in accordance with Section 208.5.2.

The corresponding reduced design seismic forces shall be
used for design in accordance with Section 203.

208.5.3.5.5 Directional Effects

Directional effects for horizontal ground motion shall
conform to the requirements of Section 208.6. The effects
of vertical ground motions on horizontal cantilevers and
pre-stressed elements shall be considered in accordance
with Section 208.6, Alternately, vertical seismic response
may be determined by dynamic response methods; in no

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-218 CHAPTER 2 - Minimum Design Loads

case shall the response used for design be less than that
obtained by the static method.

208.5.3.5.6 Torsion

The analysis shall account for torsional effects, including
accidental torsional effects as prescribed in Section
208.5.1.4. Where three-dimensional models are used for
analysis, effects of accidental torsion shall be accounted for
by appropriate adjustments in the model such as adjustment
of mass locations, or by equivalent static procedures such
as provided in Section 208.5.1.3.

208.5.3.5.7 Dual Systems

Where the lateral forces are resisted by a dual system as
defined in Section 208.4.6.4, the combined system shall be
capable of resisting the base shear determined in
accordance with this section. The moment-resisting frame
shall conform to Section 208.4.6.4, Item 2, and may be
analyzed using either the procedures of Section 208.5.2.3
or those of Section 208.5.3.5.

208.5.3.6 Time History Analysis

208.5.3.6.1 Time History

Time-history analysis shall be performed with pairs of
appropriate horizontal ground-motion time- history
components that shall be selected and scaled from not less
than three recorded events. Appropriate time histories shall
have magnitudes, fault distances and source mechanisms
that are consistent with those that control the design-basis
earthquake (or maximum capable earthquake). Where
three appropriate recorded ground-motion time-history
pairs are not available, appropriate simulated ground-
motion time-history pairs may he used to make up the total
number required. For each pair of horizontal ground-
motion components, the square root of the sum of the
squares (SRSS) of the 5 percent-damped site-specific
spectrum of the scaled horizontal components shall be
constructed. The motions shall be scaled such that the
average value of the SRSS spectra does not fall below 1.4
times the 5 percent-damped spectrum of the design-basis
earthquake for periods from 0 . 2 T second to 1. 57 seconds.
Each pair of time histories shall be applied simultaneously
to the model considering torsional effects.

The parameter of interest shall be calculated for each time-
history analysis. If three time-history analyses are
performed, then the maximum response of the parameter
of interest shall be used for design. If seven or more time-
history analyses are performed, then the average value of
the response parameter of interest may be used for design.

208.5.3.6.2 Elastic Time History Analysis

Elastic time history shall conform to Sections 208.5.3.1,
208.5.3.2, 208.5.3.3, 208.5.3.5.2, 208.5.3.5.4,

208.6.5.3.5.5, 208.6.5.3.5.6, 208.5.3.5.7 and 208.5.3.6.1
and 208.6.6.1. Response parameters from elastic time-
history analysis shall be denoted as Elastic Response
Parameters. All elements shall be designed using Strength
Design. Elastic Response Parameters may be scaled in
accordance with Section 208.5.3.5.4.

208.5.3.6.3 Nonlinear Time History Analysis

208.5.3.6.3.1 Nonlinear Time History

Nonlinear time history analysis shall meet the requirements
of Section 208.4.8.4, and time histories shall be developed
and results determined in accordance with the requirements
of Section 208.5.3.6.1. Capacities and characteristics of
nonlinear elements shall be modeled consistent with test
data or substantiated analysis, considering the Importance
Factor. The maximum inelastic response displacement
shall not be reduced and shall comply with Section 208.6.5.

208.5.3.6.3.2 Design Review

When nonlinear time-history analysis is used to justify a
structural design, a design review of the lateral- force-
res i sling system shall be performed by an independent
engineering team, including persons licensed in the
appropriate disciplines and experienced in seismic analysis
methods. The lateral -force-resisting system design review
shall include, but not be limited to, the following:

1. Reviewing the development of site-specific spectra
and ground-motion time histories.

2. Reviewing the preliminary design of the lateral-force-
resisting system.

3. Reviewing the final design of the lateral-force-
resisting system and all supporting analyses.

The engineer-of-record shall submit with the plans and
calculations a statement by all members of the engineering
team doing the review stating that the above review has
been performed.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHART FR ? -- Minimum Design I oads

2-219

208.6 Earthquake Loads and Modeling
Requirements

208.6.1 Earthquake Loads

Structures shall be designed for ground motion producing
structural response and seismic forces in any horizontal
direction. The following earthquake loads shall be used in
the load combinations set forth in Section 203:

E = pE h + E v (208-18)

E m = n 0 E h (208-19)

where

r max ' s defined as the largest of the element storey shear
ratios, r h which occurs in any of the storey levels at or
below the two-thirds height level of the building.

For braced frames, the value of r i is equal to the maximum
horizontal force component in a single brace element
divided by the total storey shear.

For moment frames, r t shall be taken as the maximum of
the sum of the shears in any two adjacent columns in a
moment frame bay divided by the storey shear. For
columns common to two bays with moment-resisting
connections on opposite sides at Level i in the direction
under consideration, 70 percent of the shear in that column
may be used in the column shear summation.

E h

n n

the earthquake load on an element of the
structure resulting from the combination of
the horizontal component, E h , and the
vertical component, E v
the earthquake load due to the base shear,
V, as set forth in Section 208.5.2 or the
design lateral force, F p , as set forth in
Section 208.9

the estimated maximum earthquake force
that can be developed in the structure as set
forth in Section 208.6.1, and used in the
design of specific elements of the structure,
as specifically identified in this section
the load effect resulting from the vertical
component of the earthquake ground
motion and is equal to an addition of
0. 5 C a ID to the dead load effect, D, for
Strength Design, and may be taken as zero
for Allowable Stress Design
the seismic force amplification factor that is
required to account for structural
overstrength, as set forth in Section
208.4.10.1

Reliability/Redundancy Factor as given by
the following equation:

P = 2~

6.1

(208-20)

where

r max = the maximum element-storey shear ratio.

For a given direction of loading, the
element-storey shear ratio is the ratio of the
design storey shear in the most heavily
loaded single element divided by the total
design storey shear.

For shear walls, shall be taken as the maximum value of
the product of the wall shear multiplied by 3 /l w and
divided by the total storey shear, where l w is the length of
the wall in meter.

For dual systems, r i shall be taken as the maximum value
of r t as defined above considering all lateral-load-resisting
elements. The lateral loads shall be distributed to elements
based on relative rigidities considering the interaction of
the dual system. For dual systems, the value of p need not
exceed 80 percent of the value calculated above.

p shall not be taken less than 1.0 and need not be greater
than 1.5. For special moment-resisting frames, except
when used in dual systems, p shall not exceed 1.25. The
number of bays of special moment-resisting frames shall
be increased to reduce r, such that p is less than or equal
to 1.25.

Exception:

Ab may be taken as the average floor area in the upper
setback portion of the building where a larger base area
exists at the ground floor.

When calculating drift, or when the structure is located in
Seismic Zone 2, p shall be taken equal to 1.0.

The ground motion producing lateral response and design
seismic forces may be assumed to act non-concurrently in
the direction of each principal axis of the structure, except
as required by Section 208.7.2.

Seismic dead load, W , is the total dead load and applicable
portions of other loads listed below.

I , In storage and warehouse occupancies, a minimum of
25 percent of the floor live load shall be applicable.

For any given Storey Level i , the element- storey shear ratio
is denoted as r*. The maximum element-storey shear ratio

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-220 CHAPTER 2 - Minimum Design Loads

2. Where a partition load is used in the floor design, a
load of not less than 0.5 kN/m 2 shall be included.

3. Total weight of permanent equipment shall be
included.

208.6.2 Modeling Requirements

The mathematical model of the physical structure shall
include all elements of the lateral-force-resisting system.
The model shall also include the stiffness and strength of
elements, which are significant to the distribution of forces,
and shall represent the spatial distribution of the mass and
stiffness of the structure. In addition, the model shall
comply with the following:

1 . Stiffness properties of reinforced concrete and
masonry elements shall consider the effects of cracked
sections.

2. For steel moment frame systems, the contribution of
panel zone deformations to overall storey drift shall be
included.

208.6.3 PA Effects

The resulting member forces and moments and the storey
drifts induced by PA effects shall be considered in the
evaluation of overall structural frame stability and shall be
evaluated using the forces producing the displacements of
A s . PA need not be considered when the ratio of secondary
moment to primary moment does not exceed 0.10; the ratio
may be evaluated for any storey as the product of the total
dead and floor live loads, as required in Section 203, above
the storey times the seismic drift in that storey divided by
the product of the seismic shear in that storey times the
height of that storey. In Seismic Zone 4, PA need not be
considered when the storey drift ratio does not exceed

0.02/P.

208.6.4 Drift

Drift or horizontal displacements of the structure shall be
computed where required by this code. For both Allowable
Stress Design and Strength Design, the Maximum Inelastic
Response Displacement, A w , of the structure caused by the
Design Basis Ground Motion shall be determined in
accordance with this section. The drifts corresponding to
the design seismic forces of Section 208.5.2.1 or Section
208.5.3.5, A 5 , shall be determined in accordance with
Section 208.6.4.1. To determine A M , these drifts shall be
amplified in accordance with Section 208.6.4.2.

208.6.4.1 Determination of A s

A static, elastic analysis of the lateral force-resisting
system shall be prepared using the design seismic forces
from Section 208.5.2.1. Alternatively, dynamic analysis
may be performed in accordance with Section 208.5.3.
Where Allowable Stress Design is used and where drift is
being computed, the load combinations of Section 203.3
shall be used. The mathematical model shall comply with
Section 208.6.2. The resulting deformations, denoted as
A 5 , shall be determined at all critical locations in the
structure. Calculated drift shall include translational and
torsional deflections.

208.6.4.2 Determination of A M

The Maximum Inelastic Response Displacement, A M , shall
be computed as follows:

A m = 0. 7RA S (208-21)

Exception:

Alternatively , A m may be computed by nonlinear time
history analysis in accordance with Section 208.5. 3.6.3.

The analysis used to determine the Maximum Inelastic
Response Displacement A M shall consider PA effects.

208.6.5 Storey Drift Limitation

Storey drifts shall be computed using the Maximum
Inelastic Response Displacement, A M .

208.6.5.1 Calculated

Calculated storey drift using A M shall not exceed 0.025
times the storey height for structures having a fundamental
period of less than 0.7 sec. For structures having a
fundamental period of 0.7 sec or greater, the calculated
storey drift shall not exceed 0.020 times the storey height.

Exceptions:

1. These drift limits may be exceeded when it is
demonstrated that greater drift can be tolerated by
both structural elements and nonstructural elements
that could affect life safety. The drift used in this
assessment shall be based upon the Maximum
Inelastic Response Displacement , A M .

2. There shall be no drift limit in single-storey steel-
framed structures whose primary use is limited to
storage, factories or workshops. Minor accessory
uses shall be allowed. Structures on which this
exception is used shall not have equipment attached to

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-221

the structural frame or shall have such equipment
detailed to accommodate the additional drift . Walls
that are laterally supported by the steel frame shall be
designed to accommodate the drift in accordance with
Section 208. 7.2.3 .

208.6.5.2 Limitations

The design lateral forces used to determine the calculated
drift may disregard the limitations of Equations. 208-11
and 208-10 and may be based on the period determined
from Equations. 208-14 neglecting the 30 or 40 percent
limitations of Section 208.5.2.2.

208.6.6 Vertical Component

The following requirements apply in Seismic Zone 4 only.
Horizontal cantilever components shall be designed for a
net upward force of 0. 7C a IW p .

In addition to all other applicable load combinations,
horizontal pre-stressed components shall be designed using
not more than 50 percent of the dead load for the gravity
load, alone or in combination with the lateral force effects.

208.7 Detailed Systems Design Requirements

208.7.1 General

All structural framing systems shall comply with the
requirements of Section 208.4. Only the elements of the
designated seismic-force-resisting system shall be used to
resist design forces. The individual components shall be
designed to resist the prescribed design seismic forces
acting on them. The components shall also comply with the
specific requirements for the material contained in
Chapters 4 through 7. In addition, such framing systems
and components shall comply with the detailed system
design requirements contained in Section 208.7.

All building components in Seismic Zones 2 and 4 shall be
designed to resist the effects of the seismic forces
prescribed herein and the effects of gravity loadings from
dead and floor live loads.

Consideration shall be given to design for uplift effects
caused by seismic loads.

In Seismic Zones 2 and 4, provision shall be made for the
effects of earthquake forces acting in a direction other than
the principal axes in each of the following circumstances:

1. The structure has plan irregularity Type 5 as given in
Table 208-10.

2. The structure has plan irregularity Type 1 as given in
Table 208-10 for both major axes.

3. A column of a structure forms part of two or more
intersecting lateral-force-resisting systems.

Exception:

If the axial load in the column due to seismic forces acting
in either direction is less than 20 percent of the column
axial load capacity.

The requirement that orthogonal effects be considered may
be satisfied by designing such elements for 100 percent of
the prescribed design seismic forces in one direction plus
30 percent of the prescribed design seismic forces in the
perpendicular direction. The combination requiring the
greater component strength shall be used for design.
Alternatively, the effects of the two orthogonal directions
may be combined on a square root of the sum of the squares
(SRSS) basis. When the SRSS method of combining
directional effects is used, each term computed shall be
assigned the sign that will result in the most conservative
result.

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122 CHAPTER 2 - Minimum Design Loads

8.7.2 Structural Framing Systems

ur types of general building framing systems defined in
ction 208.4.6 are recognized in these provisions and
Dwn in Table 208-11. Each type is subdivided by the
)es of vertical elements used to resist lateral seismic
*ces. Special framing requirements are given in this
:tion and in Chapters 4 through 7.

8.7.2.1 Detailing for Combinations of Systems

r components common to different structural systems,
; more restrictive detailing requirements shall be used.

8.7.2.2 Connections

mnections that resist design seismic forces shall be
signed and detailed on the drawings.

8.7.2.3 Deformation Compatibility

1 structural framing elements and their connections, not
luired by design to be part of the lateral-force-resisting
stem, shall be designed and/or detailed to be adequate to
iintain support of design dead plus live loads when
bjected to the expected deformations caused by seismic
rces. PA effects on such elements shall be considered.
;pected deformations shall be determined as the greater

of the Maximum Inelastic Response Displacement, A Ms
considering PAD effects determined in accordance with
Section 208.6.4.2 or the deformation induced by a storey
drift of 0.0025 times the storey height. When computing
expected deformations, the stiffening effect of those
elements not part of the lateral-force-resisting system shall
be neglected.

For elements not part of the lateral-force-resisting system,
the forces inducted by the expected deformation may be
considered as ultimate or factored forces. When computing
the forces induced by expected deformations, the
restraining effect of adjoining rigid structures and
nonstructural elements shall be considered and a rational
value of member and restraint stiffness shall be used.
Inelastic deformations of members and connections may be
considered in the evaluation, provided the assumed
calculated capacities are consistent with member and
connection design and detailing.

For concrete and masonry elements that are part of the
lateral- force-resisting system, the assumed flexural and
shear stiffness properties shall not exceed one half of the
gross section properties unless a rational cracked-section
analysis is performed. Additional deformations that may
result from foundation flexibility and diaphragm
deflections shall be considered. For concrete elements not
part of the lateral-force-resisting system, see Section 42 1 .9.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-223

Table 208-1 1A Earthquake-Force-Resisting Structural Systems of Concrete

Basic Seismic-Force Resisting System

n 0

System Limitation and
Building Height Limitation by
Seismic Zone, m

Zone 2

Zone 4

A. Bearing Wall Systems

• Special reinforced concrete shear walls

4.5

2.8

• Ordinary reinforced concrete shear walls

4.5

2.8

B. Building Frame Systems

• Special reinforced concrete shear walls or braced
frames (shear walls)

5.0

2.8

• Ordinary reinforced concrete shear walls or braced
frames

5.6

2.2

• Intermediate precast shear walls or braced frames

5.0

2.5

C. Moment-Resisting Frame Systems

• Special reinforced concrete moment frames

8.5

2.8

• Intermediate reinforced concrete moment frames

5.5

2.8

• Ordinary reinforced concrete moment frames

3.5

2.8

D . Dual Systems

• Special reinforced concrete shear walls

8.5

2.8

• Ordinary reinforced concrete shear walls

6.5

2.8

E. Dual System with Intermediate Moment Frames

• Special reinforced concrete shear walls

6.5

2.8

• Ordinary reinforced concrete shear walls

5.5

2.8

• Shear wall frame interactive system with ordinary
reinforced concrete moment frames and ordinary
reinforced concrete shear walls

4.2

2.8

F. Cantilevered Column Building Systems

• Cantilevered column elements

2.2

2.0

G. Shear Wall- Frame Interaction Systems

5.5

2.8

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-224 CHAPTER 2 - Minimum Design Loads

Table 208-1 IB Earthquake-Force-Resisting Structural Systems of Steel

Basic Seismic-Force Resisting System

n 0

System Limitation and
Building Height Limitation by
Seismic Zone, m

Zone 2

Zone 4

A. Bearing Wall Systems

• Light steel-framed bearing walls with tension-only
bracing

2.8

2.2

• Braced frames where bracing carries gravity load

4.4

2.2

• Light framed walls sheathed with steel sheets
structural panels rated for shear resistance or steel
sheets

5.5

2.8

• Light-framed walls with shear panels of all other
light materials

4.5

2.8

• Light-framed wall systems using flat strap bracing

2.8

2.2

B. Building Frame Systems

• Steel eccentrically braced frames (EBF), moment-
resist in g connections at columns away from links

8.0

2.8

* Steel eccentrically braced frames (EBF), non-
moment-resisting connections at columns away
from links

6.0

2.2

• Special concentrically braced frames (SCBF)

6.0

2.2

• Ordinary concentrically braced frames (OCBF)

3.2

2.2

• Light-framed walls sheathed with steel sheet
structural panels / sheet steel panels

6.5

2.8

• Light frame walls with shear panels of all other
materials

2.5

2.8

• Buckling-restrained braced frames (BRBF), non-
moment-resisting beam-column connection

7.0

2.8

• Buckling-restrained braced frames, moment-
resisting beam-column connections

8.0

2.8

• Special steel plate shear walls (SPSW)

7.0

2.8

C, Moment-Resisting Frame Systems

• Special moment-resisting frame (SMRF)

8.0

3.0

• Intermediate steel moment frames ( 1 Mb')

4.5

3.0

• Ordinary moment frames (OMF)

3.5

3.0

• Special truss moment frames (STMF)

6.5

3.0

• Special composite steel and concrete moment
frames

8.0

3.0

• Intermediate composite moment frames

5.0

3.0

• Composite partially restrained moment frames

6.0

3.0

• Ordinary composite moment frames

3.0

D. Dual Systems with Special Moment Frames

• Steel eccentrically braced frames

8.0

2.8

• Special steel concentrically braced frames

7.0

2.8

• Composite steel and concrete eccentrically braced
frame

8.0

2.8

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-225

Table 208-1 IB (continued) Earthquake-Force-Resisting Structural Systems of Steel

Basic Seismic-Force Resisting System

I2 0

System Limitation and
Building Height
Limitation by Seismic
Zone, m

Zone 2

Zone 4

• Composite steel and concrete concentrically braced
frame

6.0

2.8

• Composite steel plate shear walls

7.5

2.8

• Buckling-restrained braced frame

8.0

2.8

• Special steel plate shear walls

8.0

2.8

• Masonry shear wall with steel OMRF

4.2

2.8

• Steel EBF with steel SMRF

8.5

2.8

• Steel EBF with steel OMRF

4.2

2.8

• Special concentrically braced frames with steel

SMRF

7.5

2.8

• Special concentrically braced frames with steel

OMRF

4.2

2.8

E. Dual System with Intermediate Moment Frames

• Special steel concentrically braced frame

6.0

2.8

• Composite steel and concrete concentrically braced
frame

5.5

2.8

• Ordinary composite braced frame

3.5

2.8

• Ordinary composite reinforced concrete shear walls
with steel elements

5.0

3.0

F, Cantilevered Column Building Systems

• Special steel moment frames

2.2

2.0

• Intermediate steel moment frames

1.2

2.0

• Ordinary steel moment frames

1.0

2.0

• Cantilevered column elements

2.2

2.0

(7. Steel Systems not Specifically Detailed for Seismic
Resistance , Excluding Cantilever Systems

3.0

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2-226 CHAPTER 2 - Minimum Design Loads

Table 208-1 1C Earthquake-Force- Resisting Structural Systems of Masonry

Basic Seismic-Force Resisting System

f2 0

System Limitation and
Building Height Limitation by
Seismic Zone, m

Zone 2

Zone 4

A. Bearing Wall Systems

• Masonry shear walls

4.5

2.8

B . Building Frame Systems

• Masonry shear walls

5.5

2.8

C. Moment-Resisting Frame Systems

• Masonry moment-resisting wall frames (MMRWF)

6.5

2.8

D. Dual Systems

• Masonry shear walls with SMRF

5.5

2.8

• Masonry shear walls with steel OMRF

4.2

2.8

• Masonry shear walls with concrete IMRF

4.2

2.8

• Masonry shear walls with masonry MMRWF

6.0

2.8

Table 208-1 ID Earthquake-Force-Resisting Structural Systems of Wood

Basic Seismic-Force Resisting System

n 0

System Limitation and
Building Height Limitation by
Seismic Zone (meters)

Zone 2

Zone 4

A. Bearing Wall Systems

• Light-framed walls with shear panels: wood

structural panel walls for structures three stories or
less

5.5

2.8

• Heavy timber braced frames where bracing carries
gravity load

2.8

2.2

• All other light framed walls

B. Building Frame Systems

• Ordinary heavy timber-braced frames

5.6

2.2

* NL

208.7.2.3.1 Adjoining Rigid Elements

Moment-resisting frames and shear walls may be enclosed
by or adjoined by more rigid elements; provided it can be
shown that the participation or failure of the more rigid
elements will not impair the vertical and lateral- load-
resisting ability of the gravity load and lateral-force-
resisting systems. The effects of adjoining rigid elements
shall be considered when assessing whether a structure
shall be designated regular or irregular in Section 208.4.5.

208.7.2.3.2 Exterior Elements

Exterior non-bearing, non-shear wall panels or elements
that are attached to or enclose the exterior shall be designed
to resist the forces per Equation 208-27 or 208-28 and shall
accommodate movements of the structure based on and
temperature changes. Such elements shall be supported by
means of cast-in-place concrete or by mechanical

connections and fasteners in accordance with the following
provisions:

1. Connections and panel joints shall allow for a relative
movement between stories of not less than two times
storey drift caused by wind, the calculated storey drift
based on or 12.7 mm, whichever is greater.

2. Connections to permit movement in the plane of the
panel for storey drift shall be sliding connections using
slotted or oversize holes, connections that permit
movement by bending of steel, or other connections
providing equivalent sliding and ductility capacity.

3. Bodies of connections shall have sufficient ductility
and rotation capacity to preclude fracture of the
concrete or brittle failures at or near welds.

Association of Structural Engineers of the Philippines, Inc (ASEP)

CHAPTER 2 - Minimum Design Loads 2-227

other elements of the lateral-force-resisting system. For
Allowable Stress Design, the design strength may be
determined using an allowable stress increase of 1.7 and a
resistance factor, 0 , of 1.0. This increase shall not be
combined with the one-third stress increase permitted by
Section 203.4, but may be combined with the duration of
load increase permitted in Section 615.3.4.

208.7.2.5 Concrete Frames

Concrete frames required by design to be part of the lateral-
force-resisting system shall conform to the following:

4. The body of the connection shall be designed for the
force determined by Equation 208-28, where R p =

3. 0 and a p = 1. 0.

5. All fasteners in the connecting system, such as bolts,
inserts, welds and dowels, shall be designed for the
forces determined by Equation 208-28, where R p =

1. 0 and a p = 1. 0.

6. Fasteners embedded in concrete shall be attached to,
or hooked around, reinforcing steel or otherwise
terminated to effectively transfer forces to the
reinforcing steel.

208.7.2.3.3 Ties and Continuity

All parts of a structure shall be interconnected and the
connections shall be capable of transmitting the seismic
force induced by the parts being connected. As a minimum,
any smaller portion of the building shall be tied to the
remainder of the building with elements having at least
strength to resist 0. 5C a I times the weight of the smaller
portion.

A positive connection for resisting horizontal force acting
parallel to the member shall be provided for each beam,
girder or truss. This force shall not be less than 0.3C a 7
times the dead plus live load.

208.7.2.4 Collector Elements

Collector elements shall be provided that are capable of
transferring the seismic forces originating in other portions
of the structure to the element providing the resistance to
those forces.

Collector elements, splices and their connections to
resisting elements shall resist the forces determined in
accordance with Equation 208-22. In addition, collector
elements, splices, and their connections to resisting
elements shall have the design strength to resist the
combined loads resulting from the special seismic load of
Section 203.5.

Exception:

In structures, or portions thereof, braced entirely by light-
frame wood shear walls or light-frame steel and wood
structural panel shear wall systems, collector elements,
splices and connections to resisting elements need only be
designed to resist forces in accordance with Equation 208-
22 .

The quantity E M need not exceed the maximum force that
can be transferred to the collector by the diaphragm and

1. In Seismic Zone 4 they shall be special moment-
resisting frames.

2. In Seismic Zone 2 they shall, as a minimum, be
intermediate moment-resisting frames.

208.7.2.6 Anchorage of Concrete or Masonry Walls

Concrete or masonry walls shall be anchored to all floors
and roofs that provide out-of-plane lateral support of the
wall. The anchorage shall provide a positive direct
connection between the wall and floor or roof construction
capable of resisting the larger of the horizontal forces
specified in this section and Sections 206.4 and 208.9. In
addition, in Seismic Zone 4, diaphragm to wall anchorage
using embedded straps shall have the straps attached to or
hooked around the reinforcing steel or otherwise
terminated to effectively transfer forces to the reinforcing
steel. Requirements for developing anchorage forces in
diaphragms are given in Section 208.7.2.6. Diaphragm
deformation shall be considered in the design of the
supported walls.

208.7.2.6.1 Out-of-Plane Wall Anchorage to
Flexible Diaphragms

This section shall apply in Seismic Zone 4 where flexible
diaphragms, as defined in Section 208.5. 1 .3, provide lateral
support for walls.

1. Elements of the wall anchorage system shall be
designed for the forces specified in Section 208.9
where R p = 3. 0 and a p = 1. 5.

2. In Seismic Zone 4, the value of F p used for the design
of the elements of the wall anchorage system shall not
be less than 6. 1 kN per lineal meter of wall substituted
for E.

3. See Section 206.4 for minimum design forces in other
seismic zones.

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2-228 CHAPTER 2 - Minimum Design Loads

4. When elements of the wall anchorage system are not
loaded concentrically or are not perpendicular to the
wall, the system shall be designed to resist all
components of the forces induced by the eccentricity.

5. When pilasters are present in the wall, the anchorage
force at the pilasters shall be calculated considering
the additional load transferred from the wall panels to
the pilasters. However, the minimum anchorage force
at a floor or roof shall be that specified in Section
208.7.2.7, Item 2.

6. The strength design forces for steel elements of the
wall anchorage system shall be 1 .4 times the forces
otherwise required by this section.

7. The strength design forces for wood elements of the
wall anchorage system shall be 0.85 times the force
otherwise required by this section and these wood
elements shall have a minimum actual net thickness of
63.5 mm.

accordance with Section 208.5.2 using a R no ^
exceeding 4.

4. Diaphragms supporting concrete or masonry walls
shall have continuous ties or struts between diaphragm
chords to distribute the anchorage forces specified in
Section 208.7.2.7. Added chords of subdiaphragms
may be used to form subdiaphragms to transmit the
anchorage forces to the main continuous crossties. The
maximum length-to-width ratio of the wood structural
sub-diaphragm shall be 2 l A:l.

5. Where wood diaphragms are used to laterally support
concrete or masonry walls, the anchorage shall
conform to Section 208.7.2.7. In Seismic Zone 2 and
4, anchorage shall not be accomplished by use of
toenails or nails subject to withdrawal, wood ledgers
or framing shall not be used in cross-grain bending or
cross-grain tension, and the continuous ties required
by Item 4 shall be in addition to the diaphragm
sheathing.

208.7.2.7 Diaphragms

1 . The deflection in the plane of the diaphragm shall not
exceed the permissible deflection of the attached
elements. Permissible deflection shall be that
deflection that will permit the attached element to
maintain its structural integrity under the individual
loading and continue to support the prescribed loads.

2. Floor and roof diaphragms shall be designed to resist
the forces determined in accordance with the
following equation:

1 px

Iu=x w i

— Wpx

(208-22)

The force F px determined from Equation 208-22 need
not exceed 1.0 C a Iw px , but shall not be less than

0 . 5C a Iw px .

When the diaphragm is required to transfer design
seismic forces from the vertical-resisting elements
above the diaphragm to other vertical-resisting
elements below the diaphragm due to offset in the
placement of the elements or to changes in stiffness in
the vertical elements, these forces shall be added
to those determined from Equation 208-22.

6. Connections of diaphragms to the vertical elements in
structures in Seismic Zone 4, having a plan irregularity
of Type 1, 2, 3 or 4 in Table 208-10, shall be designed
without considering either the one-third increase or the
duration of load increase considered in allowable
stresses for elements resisting earthquake forces.

7. In structures in Seismic Zone 4 having a plan
irregularity of Type 2 in Table 208-10, diaphragm
chords and drag members shall be designed
considering independent movement of the projecting
wings of the structure. Each of these diaphragm
elements shall be designed for the more severe of the
following two assumptions:

a. Motion of the projecting wings in the same
direction.

b. Motion of the projecting wings in opposing
directions.

Exception:

This requirement may be deemed satisfied if the procedures
of Section 208,5.3 in conjunction with a three-dimensional
model have been used to determine the lateral seismic
forces for design.

208.7.2.8 Framing below the Base

3. Design seismic forces for flexible diaphragms
providing lateral supports for walls or frames of
masonry or concrete shall be determined using
Equation 208-22 based on the load determined in

The strength and stiffness of the framing between the base
and the foundation shall not be less than that of the
superstructure. The special detailing requirements of
Chapters 4, 5 and 7, as appropriate, shall apply to columns

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CHAPTER 2 - Minimum Design Loads 2-229

supporting discontinuous lateral-force-resisting elements
and to SMRF, IMRF, EBF, STMF and MMRWF system
elements below the base, which are required to transmit the
forces resulting from lateral loads to the foundation.

208.7.2.9 Building Separations

All structures shall be separated from adjoining structures.
Separations shall allow for the displacement A m . Adjacent
buildings on the same property shall be separated by at
least A MT where

A mt — V (A M i) + (A M2 ) 2 (208-23)

and A M1 and A M2 are the displacements of the adjacent
buildings.

When a structure adjoins a property line not common to a
public way, that structure shall also be set back from the
property line by at least the displacement A M of that
structure.

Exception:

Smaller separations or property line setbacks may be
permitted when justified by rational analyses based on
maximum expected ground motions.

208.8 Non-Building Structures

208.8.1 General

208.8.1.1 Scope

Non-building structures include all self- supporting
structures other than buildings that carry gravity loads and
resist the effects of earthquakes. Non-building structures
shall be designed to provide the strength required to resist
the displacements induced by the minimum lateral forces
specified in this section. Design shall conform to the
applicable provisions of other sections as modified by the
provisions contained in Section 208.8.

208.8.1.2 Criteria

When applicable, design strengths and other detailed
design criteria shall be obtained from other sections or their
referenced standards. The design of non-building
structures shall use the load combinations or factors
specified in Section 203.3 or 203.4. For non-building
structures designed using Section 208.8.3, 208.8.4 or
208.8.5, the Reliability/Redundancy Factor, p, may be
taken as 1.0.

When applicable design strengths and other design criteria
are not contained in or referenced by this code, such criteria
shall be obtained from approved national standards.

208.8.1.3 Weight W

The weight, W, for non-building structures shall include all
dead loads as defined for buildings in Section 208.6.1. For
purposes of calculating design seismic forces n non-
building structures, W shall also include all normal
operating contents for items such as tanks, vessels, bins and
piping.

208.8.1.4 Period

The fundamental period of the structure shall be
determined by rational methods such as by using Method
B in Section 208.5.2.2.

208.8.1.5 Drift

The drift limitations of Section 208.6.5 need not apply to
non-building structures. Drift limitations shall be
established for structural or nonstructural elements whose
failure would cause life hazards. PA effects shall be
considered for structures whose calculated drifts exceed
the values in Section 208.6.3.

The minimum design seismic forces prescribed in this
section are at a level that produces displacements in a fixed
base, elastic model of the structure, comparable to those
expected of the real structure when responding to the
Design Basis Ground Motion. Reductions in these forces
using the coefficient R is permitted where the design of
non-building structures provides sufficient strength and
ductility, consistent with the provisions specified herein for
buildings, to resist the effects of seismic ground motions as
represented by these design forces.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-230 CHAPTER 2 - Minimum Design Loads

Table 208-12 R and ft on Factors for Non-building
Structures

STRUCTURE TYPE

1 . Vessels, including tanks and
pressurized spheres, on braced
or unbraced legs.

2.2

2.0

2. Cast-in-place concrete silos and
chimneys having walls
continuous to the foundations

3.6

2.0

3. Distributed mass cantilever
structures such as stacks,
chimneys, silos and skirt-
supported vertical vessels.

2.9

2.0

4. Trussed towers (freestanding or
guyed), guyed stacks and
chimneys.

2.9

2.0

5. Cantilevered column-type
structures.

2.2

2.0

6. Cooling towers.

3.6

2.0

7. Bins and hoppers on braced or
unbraced legs.

2.9

2.0

8. Storage racks.

3.6

2.0

9. Signs and billboards.

3.6

2.0

10. Amusement structures and
monuments.

2.2

2.0

1 1. All other self-supporting

structures not otherwise covered.

2.9

2.0

208.8.1.6 Interaction Effects

In Seismic Zone 4, structures that support flexible
nonstructural elements whose combined weight exceeds 25
percent of the weight of the structure shall be designed
considering interaction effects between the structure and
the supported elements.

208.8.2 Lateral Force

calculated member forces and moments does not exceed

2 . 8 .

208.8.3 Rigid Structures

Rigid structures (those with period T less than 0.06 s) and
their anchorages shall be designed for the lateral force
obtained from Equation 208-24.

V = 0.7C a IW (208-24)

The force V shall be distributed according to the
distribution of mass and shall be assumed to act in any
horizontal direction.

208.8.4 Tanks with Supported Bottoms

Flat bottom tanks or other tanks with supported bottoms,
founded at or below grade, shall be designed to resist the
seismic forces calculated using the procedures in Section
208.9 for rigid structures considering the entire weight of
the tank and its contents. Alternatively, such tanks may be
designed using one of the two procedures described below:

1 . A response spectrum analysis that includes
consideration of the actual ground motion anticipated
at the site and the inertial effects of the contained fluid.

2. A design basis prescribed for the particular type of
tank by an approved national standard, provided that
the seismic zones and occupancy categories shall be in
conformance with the provisions of Sections 208.4.4.2
and 208.4.4.3, respectively.

208.8.5 Other Non-building Structures

Non-building structures that are not covered by Section
208.8.3 and 208.8.4 shall be designed to resist design
seismic forces not less than those determined in accordance
with the provisions in Section 208.5 with the following
additions and exceptions:

Lateral-force procedures for non-building structures with
structural systems similar to buildings (those with
structural systems which are listed in Table 208-11) shall
be selected in accordance with the provisions of Section
208.4.

1 . The factors R and ft 0 shall be as set forth in Table
208-12. The total design base shear determined in
accordance with Section 208.5.2 shall not be less than
the following:

V = 0. 56 C a IW (208-25)

Exception:

Intermediate moment-resisting frames (IMRF) may be used
in Seismic Zone 4 for non-building structures in
Occupancy Categories III and IV if (1) the structure is less
than 15 m in height and (2) the value R used in reducing

Additionally, for Seismic Zone 4, the total base shear
shall also not be less than the following:

1.6 ZNJ

(208-26)

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CHAPTER 2 - Minimum Design Loads

2 231

2. The vertical distribution of the design seismic forces
in structures covered by this section may be
determined by using the provisions of Section
208.5.2.3 or by using the procedures of Section
208.5.3.

208.9.2 Design for Total Lateral Force

The total design lateral seismic force, F p , shall be
determined from the following equation:

Fp 4C a I p w p

(208-27)

Exception:

For irregular structures assigned to Occupancy
Categories I and II that cannot be modeled as a single
mass , the procedures of Section 208.5.3 shall be used .

3. Where an approved national standard provides a basis
for the earthquake-resistant design of a particular type
of non-building structure covered by this section, such
a standard may be used, subject to the limitations in
this section:

The seismic zones and occupancy categories shall be in
conformance with the provisions of Sections 208.4.4 and
208.4.2, respectively.

The values for total lateral force and total base overturning
moment used in design shall not be less than 80 percent of
the values that would be obtained using these provisions.

208.9 Lateral Force on Elements of Structures,
Nonstructural Components and Equipment
Supported by Structures

208.9.1 General

Elements of structures and their attachments, permanent
nonstructural components and their attachments, and the
attachments for permanent equipment supported by a
structure shall be designed to resist the total design seismic
forces prescribed in Section 208.9.2.

Attachments for floor- or roof-mounted equipment
weighing less than 1.8 kN, and furniture need not be
designed.

Attachments shall include anchorages and required
bracing. Friction resulting from gravity loads shall not be
considered to provide resistance to seismic forces.

When the structural failure of the lateral-force-resisting
systems of non-rigid equipment would cause a life hazard,
such systems shall be designed to resist the seismic forces
prescribed in Section 208.9.2.

When permissible design strengths and other acceptance
criteria are not contained in or referenced by this code, such
criteria shall be obtained from approved national standards
subject to the approval of the building official.

Alternatively, F p may be calculated using the following
equation:

tipCJp ( h x \

F r’ = \ L [ 1 + 3 f y ) W <> ^ 208 - 28 )

Except that F p shall not be less than 0. 7 C a I p W p and need
not be more than 4C a I p W p .

where

h x = the element or component attachment
elevation with respect to grade.
h x shall not be taken less than 0.0.
h r = the structure roof elevation with respect to
grade.

a p = the in-structure Component Amplification
Factor that varies from 1 .0 to 2.5,

A value for a p shall be selected from Table 208-13.
Alternatively, this factor may be determined based on the
dynamic properties or empirical data of the component and
the structure that supports it. The value shall not be taken
less than 1.0.

R p is the Component Response Modification Factor that
shall be taken from Table 208-13, except that R p for
anchorages shall equal 1 .5 for shallow expansion anchor
bolts, shallow chemical anchors or shallow cast-in-place
anchors. Shallow anchors are those with an embedment
length-to-diameter ratio of less than 8. When anchorage is
constructed of non-ductile materials, or by use of adhesive,
R p shall equal 1 .0.

The design lateral forces determined using Equation 208-
27 or 208-19 shall be distributed in proportion to the mass
distribution of the element or component.

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2-232 CHAPTER 2 - Minimum Design Loads

Forces determined using Equation 208-27 or 208-28 shall
be used to design members and connections that transfer
th&e forces to the seismic-resisting systems. Members and
connection design shall use the load combinations and
factors specified in Section 203.3 or 203.4. The
Reliability/Redundancy Factor, p, may be taken equal to
1 . 0 .

For applicable forces and Component Response
Modification Factors in connectors for exterior panels and
diaphragms, refer to Sections 208.7.2.3 and 208.7.2.7.

Forces shall be applied in the horizontal directions, which
result in the most critical loadings for design.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-233

Table 208-13 Horizontal Force Factors, a p and R p for
Elements of Structures and Nonstructural Components
and Equipment

Category

Element or
Component

CLp

R P

Footnote

1. Elements of
Structures

1 . Walls including the following

a. Unbraced
(cantilevered)
parapets

2.5

3.0

b. Exterior walls
at or above the
ground floor
and parapets
braced above
their centers
of gravity

1.0

3.0

c. All interior-
bearing and
non-bearing
walls

1.0

3.0

2. Penthouse
(except when
framed by an
extension of
the structural
frame)

2.5

4.0

3. Connections
for

prefabricated
structural
elements other
walls. See also
Section

208.7.2

1.0

3.0

Table 208-13 (continued)

Category

Element or
Component

d p

R P

Footnote

i Nonstructural
Components

1 . Exterior and interior ornamentations
and appendages.

a. Laterally
braced or
anchored to
the structural
frame at a
point below
their centers
of mass

2.5

3.0

b. Laterally
braced or
anchored to
the structural
frame at or
above their
centers of

mass

1.0

3.0

2. Signs and
billboards

2.5

3.0

3. Storage racks
(include
contents) over
1.8 m tall.

2.5

4.0

4. Permanent
floor-
supported
cabinets and
book stacks
more than 1.8
m in height
(include
contents)

1.0

3.0

5. Anchorage
and lateral
bracing for
suspended
ceilings and
light fixtures

1.0

3.0

3, 6, 7,

6. Access floor
systems

1.0

3.0

4 , 5, 9

7. Masonry or
concrete
fences over

1.8 m high

1.0

3.0

8. Partitions.

1.0

3.0

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2-234 CHAPTER 2 - Minimum Design Loads

Table 208-13 (continued)

.Category

Element or
Component

a p

R P

Footnote

3. Equipment

1 . Tanks and
vessels
(include
contents),
including
support
systems.

1.0

3.0

2. Electrical,
mechanical
and plumbing
equipment and
associated
conduit and
ductwork and
piping.

1.0

3.0

5 , 10,

If 12,
13, 14,
15, 16

3. Any flexible
equipment
laterally
braced or
anchored to
the structural
frame at a
point below
their center of

mass

2.5

3.0

5, 10,

14 ,

15, 16

4.Anchorage of
emergency
power supply
systems and
essential
communicatio
ns equipment.
Anchorage
and support
systems for
battery racks
and fuel tanks
necessary for
operation of
emergency
equipment.

Category

Element or
Component

CLp

R P

Footnote

4. Other
Components

1 . Rigid
components
with ductile
material and
attachments.

1.0

3.0

_ — -

2. Rigid
components
with

nonductile
material or
attachments

1.0

1.5

3. Flexible
components
with ductile
material and
attachments.

2.5

3.0

4. Flexible
components
with

nonductile
material or
attachments.

2.5

1.5

Notes for Table 208.13

1 See Section 208.2 for definitions of flexible components
and rigid components.

2 See Section 208.8. 7.2.3 and 208. 7.2. 7 for concrete and
masonry walls and Section 208.9.2 for connections for
panel connectors for panels.

3 Applies to Seismic Zones 2 and 4 only.

4 Ground supported steel storage racks may be designed
using the provisions of Sections 208.8. Load and
resistance factor design may be used for the design of
cold-formed steel members, provided seismic design
forces are equal to or greater than those specified in
Section 208.9.2 or 208.8.3 as appropriate.

5 Only anchorage or restraints need be designed.

6 Ceiling weight shall include all light fixtures and other
equipment or partitions that are laterally supported by
the ceiling. For purposes of determining the seismic
force, a ceiling weight of not less than 0.2 kPa shall be
used.

7 Ceilings constructed of lath and plaster or gypsum
board screw or nail attached to suspended members
that support a ceiling at one level extending from wall
to wall need not be analyzed, provided the walls are not
over 15 meters apart.

8 Light fixtures and mechanical services installed in
metal suspension systems for acoustical tile and lay-in
panel ceilings shall be independently supported from

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CHAPTER 2 - Minimum Design Loads 2-235

the structure above as specified in UBC Standard 25-2,
Part III

9 Wp for access floor systems shall be the dead load of
the access floor system plus 25 percent of the floor live
load plus a 0.5 kPa partition load allowance.

10 Equipment includes , but is not limited to, boilers,
chillers, heat exchangers, pumps, air-handling units,
cooling towers, control panels, motors, switchgear,
transformers and life-safety equipment. It shall include
major conduit, ducting and piping, which services such
machinery and equipment and fire sprinkler systems.
See Section 208.9.2 for additional requirements for
determining a p for nonrigid or flexibly mounted
equipment.

11 Seismic restraints may be omitted from piping and duct
supports if all the following conditions are satisfied:

11 1 Lateral motion of the piping or duct will not cause
damaging impact with other systems.

112 The piping or duct is made of ductile material with
ductile connections.

113 Lateral motion of the piping or duct does not cause
impact of fragile appurtenances (e.g., sprinkler heads)
with any other equipment, piping or structural member.

11 4 Lateral motion of the piping or duct does not cause
loss of system vertical support.

u 5 Rod-hung supports of less than 300 mm in length
have top connections that cannot develop moments.

11 6 Support members cantilevered up from the floor are
checked for stability.

12 Seismic restraints may be omitted from electrical
raceways, such as cable trays, conduit and bus ducts, if
all the following conditions are satisfied:

12 1 Lateral motion of the raceway will not cause
damaging impact with other systems.

12 2 Lateral motion of the raceway does not cause loss of
system vertical support.

]2J Rod-hung supports of less than 300 mm in length
have top connections that cannot develop moments.

124 Support members cantilevered up from the floor are
checked for stability.

13 Piping, ducts and electrical raceways, which must be
functional following an earthquake, spanning between
different buildings or structural systems shall be
sufficiently flexible to withstand relative motion of
support points assuming out-of phase motions.

14 Vibration isolators supporting equipment shall be
designed for lateral loads or restrained from displacing
laterally by other means. Restraint shall also be
provided, which limits vertical displacement, such that
lateral restraints do not become disengaged. a p and
R p for equipment supported on vibration isolators shall
be taken as 2.5 and 1.5, respectively, except that if the
isolation mounting frame is supported by shallow or

National Structural Code of the I

expansion anchors, the design forces for the anchors
calculated by Equations. 208-27, or 208-28 (including
limits), shall be additionally multiplied by factor of 2. 0.

15 Equipment anchorage shall not be designed such that
loads are resisted by gravity friction (e.g., friction
clips).

16 Expansion anchors, which are required to resist
seismic loads in tension, shall not be used where
operational vibrating loads are present.

17 Movement of components within electrical cabinets,
rack-and skid-mounted equipment and portions of skid-
mounted electromechanical equipment that may cause
damage to other components by displacing, shall be
restricted by attachment to anchored equipment or
support frames.

18 Batteries on racks shall be restrained against
movement in all direction due to earthquake forces.

19 Seismic restraints may include straps, chains, bolts,
barriers or other mechanisms that prevent sliding,
falling and breach of containment of flammable and
toxic materials . Friction forces may not be used to resist
lateral loads in the restraints unless positive uplift
restraint is provided which ensures that the friction
forces act continuously.

208.9.3 Specifying Lateral Forces

Design specifications for equipment shall either specify the
design lateral forces prescribed herein or reference these
provisions.

208.9.4 Relative Motion of Equipment Attachments

For equipment in Categories I and II buildings as defined
in Table 103-1, the lateral-force design shall consider the
effects of relative motion of the points of attachment to the
structure, using the drift based upon A M .

208.9.5 Alternative Designs

Where an approved national standard or approved physical
test data provide a basis for the earthquake-resistant design
of a particular type of equipment or other nonstructural
component, such a standard or data may be accepted as a
basis for design of the items with the following limitations:

1. These provisions shall provide minimum values for
the design of the anchorage and the members and
connections that transfer the forces to the seismic-
resisting system.

2. The force, F p , and the overturning moment used in the
design of the nonstructural component shall not be less
than 80 percent of the values that would be obtained
using these provisions.

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CHAPTER 2 - Minimum Design Loads

208.10 Alternative Earthquake Load Procedure

The earthquake load procedure of latest edition of
ASCE/SEI 7 prior to the release of this code may be used
in determining the earthquake loads as an alternative
procedure subject to reliable research work commissioned
by the owner or the engineer-on-record to provide for all
data required due to the non-availability of PHIVOLCS-
issued spectral acceleration maps for all areas in the
Philippines.

The engineer-on-record shall be responsible for the
spectral acceleration and other related data not issued by
PHIVOLCS used in the determination of the earthquake
loads. This alternative earthquake load procedure shall be
subject to Peer Review and approval of the Building
Official.

SECTION 209

SOIL LATERAL LOADS

209.1 General

Basement, foundation and retaining walls shall be designed
to resist lateral soil loads. Soil loads specified in Table 209-
1 shall be used as the minimum design lateral soil loads
unless specified otherwise in a soil investigation report
approved by the building official. Basement walls and
other walls in which horizontal movement is restricted at
the top shall be designed for at-rest pressure. Retaining
walls free to move and rotate at the top are permitted to be
designed for active pressure. Design lateral pressure from
surcharge loads shall be added to the lateral earth pressure
load. Design lateral pressure shall be increased if soils with
expansion potential are present at the site.

Exception:

Basement walls extending not more than 2,4 m below grade
and supporting flexible floor systems shall be permitted to
be designed for active pressure.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-237

Table 209-1 - Soil Lateral Load

Description of
Backfill Material

Unified

Soil

Classificat

ion

Design Lateral

Soil Load a
kPa per m depth

Active

pressure

At-rest

pressure

Well-graded,
clean gravels;
gravel-sand mixes

Poorly graded
clean gravels;
gravel-sand mixes

Silty gravels,
poorly graded
gravel-sand mixes

Clayey gravels,
poorly graded
gravel-and-clay
mixes

Well-graded,
clean sands;
gravelly sand
mixes

Poorly graded
clean sands; sand-
gravel mixes

Silty sands, poorly
graded sand-silt
mixes

Sand-silt clay mix
with plastic fines

SM-SC

Clayey sands,
poorly graded
sand-clay mixes

Inorganic silts and
clayey silts

Mixture of
inorganic silt and
clay

ML-CL

Inorganic clays of
low to medium
plasticity

Organic silts and
silt clays, low
plasticity

Note b

Inorganic clayey
silts, elastic silts

Note b

Inorganic clays of
high plasticity

Note b

Organic clays and
silty clays

Note b

govern. Submerged or saturated soil pressures
shall include the weight of the buoyant soil plus
the hydrostatic loads .

Unsuitable as backfdl material.

The definition and classification of soil
materials shall be in accordance with ASTM
D2487.

a Design lateral soil loads are given for moist
conditions for the specified soils at their
optimum densities. Actual field conditions shall

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2-238 CHAPTER 2 - Minimum Design Loads

SECTION 210
RAIN LOADS

210.1 Roof Drainage

Roof drainage systems shall be designed in accordance
with the provisions of the code having jurisdiction in the
area. The flow capacity of secondary (overflow) drains or
scuppers shall not be less than that of the primary drains or
scuppers.

210.2 Design Rain Loads

Each portion of a roof shall be designed to sustain the load
of rainwater that will accumulate on it if the primary
drainage system for that portion is blocked plus the
uniform load caused by water that rises above the inlet of
the secondary drainage system at its design flow.

R = 0.009(8d s + d h ) (210-1)

where

d h = additional depth of water on the undeflected
roof above the inlet of secondary drainage
system at its design flow (i.e., the hydraulic
head), mm

d s = depth of water on the undeflected roof up to
the inlet of secondary drainage system when
the primary drainage system is blocked (i.e.,
the static head), mm

R = rain load on the undeflected roof, kPa

When the phrase “undeflected roof’ is used, deflections
from loads (including dead loads) shall not be considered
when determining the amount of rain on the roof.

210.3 Ponding Instability

For roofs with a slope less than 6 mm per 300 mm, the
design calculations shall include verification of adequate
stiffness to preclude progressive deflection.

210.4 Controlled Drainage

Roofs equipped with hardware to control the rate of
drainage shall be equipped with a secondary drainage
system at a higher elevation that limits accumulation of
water on the roof above that elevation. Such roofs shall be
designed to sustain the load of rainwater that will
accumulate on them to the elevation of the secondary
drainage system plus the uniform load caused by water that
rises above the inlet of the secondary drainage system at its
design flow determined from Section 210.2. Such roofs
shall also be checked for ponding instability in accordance
with Section 210.3.

SECTION 211
FLOOD LOADS

211.1 General

Within flood hazard areas as established in Section 21 1.3,
all new construction of buildings, structures and portions
of buildings and structures, including substantial
improvement and restoration of substantial damage to
buildings and structures, shall be designed and constructed
to resist the effects of flood hazards and flood loads. For
buildings that are located in more than one flood hazard
area, the provisions associated with the most restrictive
flood hazard area shall apply.

211.2 Definitions

The following words and terms shall, for the purposes of
this section, have the meanings shown herein.

BASE FLOOD refers to flood having a 1 -percent chance
of being equaled or exceeded in any given year.

BASE FLOOD ELEVATION (BFE) is the elevation of
the base flood, m, including wave height, relative to the
datum to be set by the specific national or local government
agency.

BASEMENT is the portion of a building having its floor
subgrade (below ground level) on all sides.

DESIGN FLOOD is the flood associated with the greater
of the following two areas:

1 . Area with a flood plain subject to a 1 -percent or greater
chance of flooding in any year; or

2. Area designated as a flood hazard area on a
community’s flood hazard map, or otherwise legally
designated.

DESIGN FLOOD ELEVATION (DFE) is the elevation
of the “design flood,” including wave height, m, relative to
the datum specified on the community’s legally designated
flood hazard map. The design flood elevation shall be the
elevation of the highest existing grade of the perimeter of
the building plus the depth specified on the flood hazard
map.

DRY FLOODPROOFING is a combination of design
modifications that results in a building or structure,
including the attendant utility and sanitary facilities, being
water tight with walls substantially impermeable to the
passage of water and with structural components having
the capacity to resist loads as identified in the code.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-239

EXISTING CONSTRUCTION refers to buildings and
structures for which the “start of construction” commenced
before the effective date of the ordinance or standard.
“Existing construction” is also referred to as “existing
structures.”

EXISTING STRUCTURE See “Existing construction.”

FLOOD or FLOODING is a general and temporary
condition of partial or complete inundation of normally dry
land from:

1 . The overflow of inland or tidal waters.

2. The unusual and rapid accumulation or runoff of
surface waters from any source.

FLOOD DAMAGE-RESISTANT MATERIALS are

construction material capable of withstanding direct and
prolonged contact with floodwaters without sustaining any
damage that requires more than cosmetic repair.

FLOOD HAZARD AREA refers to the greater of the
following two areas:

1 . The area within a flood plain subject to a 1 -percent or
greater chance of flooding in any year.

2. The area designated as a flood hazard area on a
community’s flood hazard map, or otherwise legally
designated.

FLOOD HAZARD AREA SUBJECT TO HIGH
VELOCITY- WAVE ACTION refers to area within the
flood hazard area that is subject to high velocity wave
action.

FLOODWAY is the channel of the river, creek or other
watercourse and the adjacent land areas that must be
reserved in order to discharge the base flood without
cumulatively increasing the water surface elevation more
than a designated height.

LOWEST FLOOR refers to the floor of the lowest
enclosed area, including basement, but excluding any
unfinished or flood-resistant enclosure, usable solely for
vehicle parking, building access or limited storage
provided that such enclosure is not built so as to render the
structure in violation of this section.

START OF CONSTRUCTION refers to the date of
permit issuance for new construction and substantial
improvements to existing structures, provided the actual
start of construction, repair, reconstruction, rehabilitation,
addition, placement or other improvement is within 180
days after the date of issuance. The actual start of

construction means the first placement of permanent
construction of a building (including a manufactured
home) on a site, such as the pouring of a slab or footings,
installation of pilings or construction of columns.
Permanent construction does not include land preparation
(such as clearing, excavation, grading or filling), the
installation of streets or walkways, excavation for a
basement, footings, piers or foundations, the erection of
temporary forms or the installation of accessory buildings
such as garages or sheds not occupied as dwelling units or
not part of the main building. For a substantial
improvement, the actual “start of construction” means the
first alteration of any wall, ceiling, floor or other structural
part of a building, whether or not that alteration affects the
external dimensions of the building.

SUBSTANTIAL DAMAGE refers to damage to any
origin sustained by a structure whereby the cost of
restoring the structure to its before-damaged condition
would equal or exceed 50 percent of the market value of
the structure before the damage occurred.

SUBSTANTIAL IMPROVEMENT refers to any repair,
reconstruction, rehabilitation, addition or improvement of
a building or structure, the cost of which equals or exceeds
50 percent of the market value of the structure before the
improvement or repair is started. If the structure has
sustained substantial damage, any repairs are considered
substantial improvement regardless of the actual repair
work performed. The term does not, however, include
either:

1 . Any project for improvement of a building required to
correct existing health, sanitary or safety code
violations identified by the building official and that
are the minimum necessary to assure safe living
conditions.

2. Any alteration of a historic structure provided that the
alteration will not preclude the structure’s continued
designation as a historic structure.

211.3 Design Requirements

2 1 1 .3. 1 Design Loads

Structural systems of buildings or other structures shall be
designed, constructed, connected, and anchored to resist
flotation, collapse, and permanent lateral displacement due
to action of flood loads associated with the design flood
(see Section 211.3.3) and other loads in accordance with
the load combinations of Section 203.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-240 CHAPTER 2 - Minimum Design Loads

211.3.2 Erosion and Scour

Tire effects of erosion and scour shall be included in the
calculation of loads on buildings and other structures in
flood hazard areas.

211.3.3 Loads on Breakaway Walls

Walls and partitions required by ASCE/SEI 24, to break
away, including their connections to the structure, shall be
designed for the largest of the following loads acting
perpendicular to the plane of the wall:

1. The wind load specified in Section 207.

2. The earthquake load specified in Section 208.

3. 0.48 kPa.

The loading at which breakaway walls are intended to
collapse shall not exceed 0.96 kPa unless the design meets
the following conditions:

1 . Breakaway wall collapse is designed to result from a
flood load less than that which occurs during the base
flood.

2. The supporting foundation and the elevated portion of
the building shall be designed against collapse,
permanent lateral displacement, and other structural
damage due to the effects of flood loads in
combination with other loads as specified in Section
203.

211.4 Loads During Flooding

211.4.1 Load Basis

In flood hazard areas, the structural design shall be based
on the design flood.

211.4.2 Hydrostatic Loads

Hydrostatic loads caused by a depth of water to the level of
the DFE shall be applied over all surfaces involved, both
above and below ground level, except that for surfaces
exposed to free water, the design depth shall be increased
by 0.30 m. Reduced uplift and lateral loads on surfaces of
enclosed spaces below the DFE shall apply only if
provision is made for entry and exit of floodwater.

211.4.3 Hydrodynamic Loads

Dynamic effects of moving water shall be determined bv
detailed analysis utilizing basic concepts of
mechanics.

Exception:

Where water velocities do not exceed 3.05 mis, dynamic
effects of moving water shall be permitted to be
converted into equivalent hydrostatic loads by
increasing the DFE for design purposes by an
equivalent surcharge depth, dh, on the headwater side .
and above the ground level only, equal to

. _aV 2 (211-1)

du — — —

where

V = average velocity of water, m/s
g = acceleration due to gravity, 9.81 m/s 2

a - coefficient of drag or shape factor (not less

than 1 .25)

The equivalent surcharge depth shall be added to the DFE
design depth and the resultant hydrostatic pressures applied
to, and uniformly distributed across, the vertical projected
area of the building or structure that is perpendicular to the
flow. Surfaces parallel to the flow or surfaces wetted by the
tail water shall be subject to the hydrostatic pressures for
depths to the DFE only.

211.4.4 Wave Loads

Wave loads shall be determined by one of the following
three methods: (1) by using the analytical procedures
outlined in this section, (2) by more advanced numerical
modeling procedures, or (3) by laboratory test procedures
(physical modeling).

Wave loads are those loads that result from water waves
propagating over the water surface and striking a building
or other structure. Design and construction of buildings and
other structures subject to wave loads shall account for the
following loads: waves breaking on any portion of the
building or structure; uplift forces caused by shoaling
waves beneath a building or structure, or portion thereof;
wave run-up striking any portion of the building or
structure; wave-induced drag and inertia forces; and wave-
induced scour at the base of a building or structure, or its
foundation. Wave loads shall be included for both V-Zones
and A-Zones. In V-Zones, waves are 0.91 m high, or
higher; in .coastal floodplains landward of the V-Zone,
waves are less than 0.91 m.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-241

Nonbreaking and broken wave loads shall be calculated
using the procedures described in Sections 211.4.2 and
211.4.3 that show how to calculate hydrostatic and
hydrodynamic loads.

Breaking wave loads shall be calculated using the
procedures described in Sections 211.4.4.1 through
211.4.4.4. Breaking wave heights used in the procedures
described in Sections 211.4.4.1 through 211.4.4.4 shall be
calculated for V-Zones and Coastal A-Zones using
Equations 211-2 and 211-3.

211.4.4.2 Breaking Wave Loads on Vertical Walls

Maximum pressures and net forces resulting from a
normally incident breaking wave (depth-limited in size,
with H b = 0.78 d s ) acting on a rigid vertical wall shall
be calculated by the following:

Pmax = C p Y*>d s + 1. 2y b) d s (21 1-5)

and

F t = 11 C pYo) d 2 s + 2. 4 Y(J) d 2 s (211-6)

H b = 0.78 d s (211-2) where

where

H b = breaking wave height, m
d s = local still water depth, m

The local still water depth shall be calculated using
Equation 211-3, unless more advanced procedures or
laboratory tests permitted by this section are used.

d s = 0.65 (BFE-G) (211-3)

where

G = ground elevation, m

Ya>

d s

maximum combined dynamic (C pYo) d s )
and static wave pressures, also

referred to as shock pressures, kN/m 2
net breaking wave force per unit length of
structure, also referred to as shock,
impulse, or wave impact force, kN/m,
acting near the still water elevation
dynamic pressure coefficient (1. 6 <

C v < 3.5) (see Table 21 1-1)
unit weight of water, kN/m3, 9.80 kN/m 3
for fresh water and 10.05 kN/m 3 for salt
water

still water depth, m at base of building or
other structure where the wave breaks

211.4.4.1 Breaking Wave Loads on Vertical Pilings and
Columns

The net force resulting from a breaking wave acting on a
rigid vertical pile or column shall be assumed to act at the
still water elevation and shall be calculated by the
following:

F D = 0.5 Yb> C D DH 2 b (211-4)

where

F d — net wave force, kN

= unit weight of water, in lb per cubic kN/m 3 ,

= 9.80 kN/m 3 for fresh water and 10.05
kN/m 3 for salt water

Yo) = unit weight of water, kN/m 3 , 9.80 kN/m 3 for
fresh water and 10.05 kN/m 3 for salt water

C D = coefficient of drag for breaking waves, =
1.75 for round piles or columns, and = 2.25
for square piles or columns

D - pile or column diameter, m for circular
sections, or for a square pile or column, 1.4
times the width of the pile or column, m

H b = breaking wave height, m

This procedure assumes the vertical wall causes a reflected
or standing wave against the waterward side of the wall
with the crest of the wave at a height of 1 .2d, above the still
water level. Thus, the dynamic static and total pressure
distributions against the wall are as shown in Figure 211-
1 .

This procedure also assumes the space behind the vertical
wall is dry, with no fluid balancing the static component of
the wave force on the outside of the wall. If free water
exists behind the wall, a portion of the hydrostatic
component of the wave pressure and force disappears (see
Figure 211-2) and the net force shall be computed by
Equation 21 1-7 (the maximum combined wave pressure is
still computed with Equation 21 1-5).

Ft = I- 1 C pYo) d 2 s + 1. 9 Yo) d 2 s (211-7)

where

F t = net breaking wave force per unit length of
structure, also referred to as shock, impulse,
or wave impact force, kN/m, acting near the
still water elevation

National Structural Code of the Philippines Volume I, 7th Edition, 2015

2-242 CHAPTER 2 - Minimum Design Loads

C p = dynamic pressure coefficient (1. 6 < C p <
3.5) (see Table 21 1-1)

, = unit weight of water, kN/m 3 , = 9.80 kN/m 3

for fresh water and 10.05 kN/m 3 for salt
water

d s = still water depth, m at base of building or
other structure where the wave breaks

211.4.4.3 Breaking Wave Loads on Non-vertical
Walls

Breaking wave forces given by Equations 21 1-6 and 21 1-7
shall be modified in instances where the walls or surfaces
upon which the breaking waves act are non-vertical. The
horizontal component of breaking wave force shall be

given by

F nv = F t sin 2 a (211-8)

where

Fnv

horizontal component of breaking wave
force, kN/m

F t

net breaking wave force acting on a vertical
surface, kN/m

a =

vertical angle between non-vertical surface
and the horizontal

211..4.4.4

Breaking Wave Loads from Obliquely
Incident Waves

Breaking wave forces given by Equations 211-6 and 211-7
shall be modified in instances where waves are obliquely
incident. Breaking wave forces from non-normally
incident waves shall be given by

F oi = F t sin 2 a (211-9)

where

F oi = horizontal component of obliquely incident
breaking wave force, kN/m

a = net breaking wave force (normally incident
waves) acting on a vertical surface, kN/m

211.4.5 Impact Loads

Impact loads are those that result from debris, ice, and any
object transported by floodwaters striking against buildings
and structures, or parts thereof Impact loads shall be
determined using a rational approach as concentrated loads
acting horizontally at the most critical location at or below
the DFE.

211.5 Establishment of Flood Hazard Areas

To establish flood hazard areas, the governing body shall
adopt a flood hazard map and supporting data. The flood
hazard map shall include, at a minimum, areas of special
flood hazard where records are available.

211.6 Design and Construction

The design and construction of buildings and structures
located in flood hazard areas, including flood hazard areas
subject to high velocity wave action.

211.7 Flood Hazard Documentation

The following documentation shall be prepared and sealed
by an engineer-of-record and submitted to the building
official:

1. For construction in flood hazard areas not subject to

high-velocity wave action:

1.1 The elevation of the lowest floor, including the
basement, as required by the lowest floor
elevation.

1.2 For fully enclosed areas below the design flood
elevation where provisions to allow for the
automatic entry and exit of floodwaters do not
meet the minimum requirements, construction
documents shall include a statement that the
design will provide for equalization of hydrostatic
flood forces.

1.3 For dry flood-proofed nonresidential buildings,
construction documents shall include a statement
that the dry flood-proofing is designed.

2. For construction in flood hazard areas subject to high-

velocity wave action:

2.1 The elevation of the bottom of the lowest
horizontal structural member as required by the
lowest floor elevation.

2.2 Construction documents shall include a statement
that the building is designed, including that the
pile or column foundation and building or
structure to be attached thereto is designed to be
anchored to resist flotation, collapse and lateral
movement due to the effects of wind and flood
loads acting simultaneously on all building
components, and other load requirements of
Section 203.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 2 - Minimum Design Loads 2-243

2.3 For breakaway walls designed to resist a nominal
load of less than 0.5 kPa or more than 1.0 kPa,
construction documents shall include a statement
that the breakaway wall is designed.

Table 211-1 Value of Dynamic Pressure Coefficient, C p

Building Category

C p

1.6

2.8

3.2

3.5

ASCE/SEI

American Society of Civil Engineers
Structural Engineering Institute
1801 Alexander Bell Drive
Reston, VA 20191-4400

ASCE/SEI 24

Section 5.3.3

Flood Resistant Design and Construction , 1998

211.8 Consensus Standards and Other Referenced
Documents

This section lists the consensus standards and other
documents which are adopted by reference within this
chapter:

Vertical Wall

Figure 211-1

Normally Incident Breaking Wave Pressures Against a Vertical Wall
(Space Behind Vertical Wall Is Dry)

National Structural Code of the Philippines Volume I, 7th Edition, 2015

-244 CHAPTER 2 - Minimum Design Loads

(Still Water Level Equal on Both Sides of Wall)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

NSCP Cl 01 -15

Chapter 3

EARTHWORKS AND
FOUNDATIONS

NATIONAL STRUCTURAL CODE OF THE PHILIPPINES
VOLUME I

BUILDINGS, TOWERS AND
OTHER VERTICAL STRUCTURES

SEVEHTH EDITION, 2015

Association of Structural Engineers of the Philippines, Inc.

Suite 713, Future Point Plaza Condominium 1
112 Panay Avenue, Quezon City, Philippines 1100

Tel. No. : (+632) 410-0483
Fax No. : (+632) 411-8606
Email: aseponline@gmail.com
Website: http://www.aseponline.org

National Structural Code of the Philippines Volume I, 7th Edition, 2015

CHAPTER 3 - Earthworks and Foundations 3-1

Table of Contents

SECTION 301 - GENERAL REQUIREMENTS

301.1 Scope

301 .2 Quality and Design

301.3 Allowable Bearing Pressures

301.4 Definitions

SECTION 302 - EXCAVATION AND FILLS

302.1 General

302.2 Cuts

302.4 Fills *

302.5 Setbacks

302.6 Drainage and Terracing

302.7 Erosion Control

SECTION 303 - FOUNDATION INVESTIGATION

303.1 General

303.2 Soil Classification _

303.3 Questionable Soils

303.4 Liquefaction Study

303.5 Expansive Soils

303.6 Compressible Soils...,*

303.7 Reports

303.8 Soil Tests

303.9 Liquefaction Potential and Soil Strength Loss ..

303.10 Adj acent Loads

303.1 1 Drainage

303.12 Plate Load Test

,3-3

,.3-3

3-3

.. ,3-3

,3-3

.....3-3

.....3-5

...3-6

.3-7

3-8

...3-8

..3-9

3-9

..,.*,3-9

...3-10

...3-12

....3-12

...3-12

SECTION 304 - ALLOWABLE FOUNDATION AND LATERAL PRESSURES .

304.1 From Geotechnical Site Investigation and Assessment

304.2 Presumptive Load-Bearing and Lateral Resisting Values "T"

304.3 Minimum Allowable Pressures

304.4 Foundations Adjacent to Existing Retaining/Basement Walls

SECTION 305 - FOOTINGS

305.1 General

305.2 Footing Design

305.4 Stepped Foundations

305.5 Footings on or Adjacent to Slopes....

305.6 Foundation Plates or Sills

305.7 Designs Employing Lateral Bearing __

305.8 Grillage Footings

305.9 Bleacher Footings _

3-12

V...342

3-13

....3-13

3-14

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-2 CHAPTER 3 - Earthworks and Foundations

SECTION 306 - PILES-GENERAL REQUIREMENTS 3-17

30&. 1 General - **■- * — ■ 3-17

306.2 Interconnection * * * 3-17

306.3 Determination of Allowable Loads * £ - * ** 3-17

306.4 Static Load Test '•>. - »-*. — — 3-18

306.5 Dynamic Load Test . .... ■«« - * * 3-18

306.6 Column Action * .......... ... - - * * 3-18

306.7 Group Action * * * * * — - 3-18

306.8 Lateral Loads — * - *»■ ■«** 3-18

306.9 Piles in Subsiding Areas - — •«* *■— * wvr. 3-19

306.10 Water Jetting * "■—* 3-19

306.10 Protection of Pile Materials .. ....... . — - * * •••.• 3-19

306.12 Allowable Loads * * * ■«* 3-19

306.13 Use of Higher Allowable Pile Stresses - * * 3-19

SECTION 307 - PILES-SPECIFIC REQUIREMENTS 3-20

307.1 Round Wood Piles - * * 3-20

307.2 Uncased Cast-In-Place Concrete Piles ............. — - * ■ 3-20

307.3 Metal-Cased Concrete Piles . * — — * — 3-20

307.4 Precast Concrete Piles - — - 3-21

307.5 Precast Prestressed Concrete Piles (Pretensioned) . * * 3-21

307.6 Structural Steel Piles....... ♦ — - 3-22

307.7 Concrete-Filled Steel Pipe Piles >*♦— . *-■**«-—** 3-22

SECTION 308 - FOUNDATION CONSTRUCTION-SEISMIC ZONE 4 3-23

308.1 General . *■■■■ ---- 3-23

308.2 Foundation and Geotechnical Investigations 3-23

308.3 Footing Foundations **■*■**•■■— 3-23

308.4 Pier and Pile Foundations * - — * * 3-23

308.5 Driven Pile Foundations — — 3-24

308.6 Cast-In-Place Concrete Foundations 3-26

SECTION 309 - SPECIAL FOUNDATION, SLOPE STABILIZATION AND MATERIALS OF
CONSTRUCTION 26

309.1 Special Foundation Systems 3-26

309.2 Acceptance and Approval 3-26

309.3 Specific Applications - *■— - »*■■* 3-26

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-3

SECTION 301

GENERAL REQUIREMENTS

301.1 Scope

This chapter sets forth requirements for excavations, fills,
footings and foundations for any building or structure.

301.2 Quality and Design

The quality and design of materials used structurally in
excavations, fills, footings and foundations shall conform to
the requirements specified in Chapters 4, 5, 6 and 7.

301.3 Allowable Bearing Pressures

Allowable stresses and design formulas provided in this
chapter shall be used with the allowable stress design load
combinations specified in Section 203.4.

301.4 Definitions

See Sections 102 and 202.

SECTION 302

EXCAVATIONS AND FILLS

302.1 General

Excavation or fills for buildings or structures shall be
constructed or protected such that they do not endanger life
or property. Reference is made to Section 109 of this code
for requirements governing excavation, grading and
earthwork construction, including fills and embankments.

302.2 Cuts

302.2.1 General

Unless otherwise recommended in the approved
geotechnical engineering report or engineering report, cuts
shall conform to the provisions of this section. In the
absence of an approved geotechnical engineering report,
these provisions may be waived for cuts 3 m or less in
height, involving intact rock or hard soil, that are not
intended to support structures.

302.2.2 Slopes

The slope of cut surfaces shall be no steeper than is safe for
the intended use and shall be no steeper than 1 unit vertical
in 2 units horizontal (50% slope) unless a geotechnical
engineering report, stating that the site has been
investigated, and giving an opinion that a cut at a steeper
slope shall be stable and not create a hazard to public or
private property, is submitted and approved. Such cuts shall
be protected against erosion or degradation by sufficient
cover, drainage, engineering and/or biotechnical means.

302.3 Excavations

302.3.1 Footings

Existing footings or foundations which may be undermined
by any excavation shall be underpinned adequately or
otherwise protected against settlement and shall be
protected against lateral movement.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-4 CHAPTER 3 - Earthworks and Foundations

302.3.2 Protection of Adjoining Property

302.3.3 Support of Excavations and Open Cuts

y The following provisions shall apply unless prevailing local Excavations or open cuts in excess of 1.5m in depth shall

laws are deemed more stringent from an engineering have adequately designed shoring or support to protect

against collapse.

standpoint:

1 . Before commencing the excavation, the person making
or causing the excavation to be made shall notify in
writing the owners of adjoining building not less than
10 days before such excavation is to be made and that
the adjoining building shall be protected. The condition
of the adjoining building shall be documented to
include photographs prior to excavation. Technical
documents pertaining to the proposed underpinning
and excavation plan shall be provided the owner of the
adjacent property.

FOR: X ■ 2 for properly compacted 1111a

FOR: a) H * 20.0m:

X ml0 ■ 1 for cuts on hard soil and
Intact rock

W, a 2.0 m:
h, s 10.0m:

| Permit Area Boundary

X mln - for loose or uncompacted soils,
a thorough soil Investigation to
be conducted by a certified
Geotechnical Engineer Is required

b) H * 20.0m:

W, 2 4.0 m:
h, s 10.0m:

1 0.6m
Imln.

| Natural or Fi nish Grade

X/"

Properly designed Interceptor
drains with outfalls spaced at
regular Intervals

F0R: a) H = height of slope

b) w i ■ width of terrace

Figure 302-1 Cut Slopes

2. Unless it can be shown through a detailed geotechnical
investigation that underpinning is unnecessary, any
person making or causing an excavation shall protect
the excavation so that the soil of adjoining property
will not cave in or settle.

In cases where the adjacent existing structure will have
more basements than the proposed building, the foundation
of the proposed building should be designed so as not to
impart additional lateral earth pressures on the existing
building (see Section 304.4).

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-5

302.4 Fills
^302.4.1 General

Unless otherwise recommended in the approved
geotechnical engineering report, fills shall conform to the
provisions of this section. In the absence of an approved
geotechnical engineering report or engineering report, these
provisions may be waived for minor fills (H < 2.0 m) not
intended to support structures.

Fills to be used to support the foundations of any building
or structure shall be placed in accordance with accepted
engineering practice. A geotechnical investigation report
and a report of satisfactory placement of fill, both
acceptable to the building official, shall be submitted when
required by the building official

No fill or other surcharge loads shall be placed adjacent to
any building or structure unless such building or structure is
capable of withstanding the additional vertical and
horizontal loads caused by the fill or surcharge.

Fill slopes shall not be constructed on natural slopes steeper
than 1 unit vertical in 2 units horizontal (50% slope).

302.4.2 Preparation of Ground

The existing ground surface shall be adequately prepared to
receive fill by removing any deleterious materials,
non-complying fill, topsoil and other unsuitable materials,
and by scarifying to provide a bond with the new fill.

Where the natural slopes are steeper than 1 unit vertical in
5 units horizontal (20% slope) and the height is greater than
1.5 m, the ground surface shall be prepared by benching
into sound bedrock or other competent material as
determined by the geotechnical engineer. The bench under
the toe of a fill on a slope steeper than 1 unit vertical in
5 units horizontal (20% slope) shall be at least 3 m wide.

The area beyond the toe of fill shall be sloped to drain or a
paved drain shall be provided. When fill is to be placed
over a cut, the bench under the toe of fill shall be at least
3 m wide but the cut shall be made before placing the fill
and acceptance by the geotechnical engineer as a suitable
foundation for fill.

302.4.3 Fill Material

Any organic or deleterious material shall be removed and
will not be permitted in fills. Except as permitted by the
geotechnical engineer, no rock or similar irreducible
material with a maximum dimension greater than 200 mm
shall be buried or placed in fills.

Exception:

The placement of larger rock may be permitted when the
geotechnical engineer properly devises a method of
placement, and continuously inspects its placement and
approves the fill stability . The following conditions shall
also apply:

1 . Prior to issuance of the grading permit, potential rock
disposal areas shall be delineated on the grading plan .

2. Rock sizes greater than 300 mm in maximum
dimension shall be 3 m or more below grade, measured
vertically.

3. Rocks shall be placed so as to assure filling of all voids
with well-graded soil.

302.4.4 Compaction

All fills shall be compacted in litis not exceeding 20 cm in
thickness to a minimum of 90 percent of maximum density
as determined by ASTM Standard D-1557. In-place density
shall be determined in accordance with ASTM D-1556,
D-2167, D-2922, D-3017 or equivalent. For clean granular
materials, the use of the foregoing procedures is
inappropriate. Relative density criteria shall be used based
on ASTM D5030-04. A minimum of three tests for every
500 m 2 area should be performed for every lift to verify
compliance with compaction requirements.

302.4.5 Slope

The slope of fill surfaces shall be no steeper than is safe for
the intended use. Fill slopes shall be no steeper than 1 unit
vertical in 2 units horizontal (50% slope) unless
substantiating data justifying steeper slopes are submitted
and approved.

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3-6 CHAPTER 3 - Earthworks and Foundations

302.5 Setbacks

302.5.1 General

Cut and fill slopes shall be set back from site boundaries in
accordance with this section subject to verification with
detailed slope stability study. Setback dimensions shall be
horizontal distances measured perpendicular to the site
boundary. Setback dimensions shall be as shown in
Figure 302-1.

302.5.2 Top of Cut Slope

The top of cut slopes shall not be made nearer to a site
boundary line than one fifth of the vertical height of cut
with a minimum of 0.6 m and a maximum of 3 m. The
setback may need to be increased for any required
interceptor drains.

302.5.3 Toe of Fill Slope

The toe of a fill slope shall be made not nearer to the site
boundary line than one half the height of the slope with a
minimum of 0.6 m and a maximum of 6 m. Where a fill
slope is to be located near the site boundary and the
adjacent off-site property is developed, special precautions
shall be incorporated in the work as the building official
deems necessary to protect the adjoining property from
damage as a result of such grading. These precautions may
include but are not limited to:

1. Additional setbacks.

2. Provision for retaining or slough walls.

3. Mechanical stabilization or chemical treatment of the
fill slope surface to minimize erosion.

4. Rockfall protection

5. Provisions for the control of surface subsurface waters.

302.5.4 Modification of Slope Location

The building official may approve alternate setbacks. The
building official may require an investigation and
recommendation by a qualified geotechnical engineer to
demonstrate that the intent of this section has been satisfied.

302.6 Drainage and Terracing

302.6.1 General

Unless otherwise indicated on the approved grading plan,
drainage facilities and terracing shall conform to the
provisions of this section for cut or fill slopes steeper than
1 unit vertical in 3 units horizontal (33.3% slope).

302.6.2 Terraces

Terraces at least 2.0m in width shall be established at not
more than 10.0m vertical intervals on all cut or fill slopes to
control surface drainage and debris except that where only
one terrace is required, it shall be at mid-height. For cut or
fill slopes greater than 20.0m in vertical height, terraces at
least 4.0m in width shall be established at not more than
10.0m vertical intervals. Terrace widths and vertical
spacing for cut and fill slopes greater than 40.0m in height
shall be designed by the Geotechnical Engineer and
approved by the Building Official. Suitable access shall be
provided to permit proper cleaning and maintenance.

Swales or ditches on terraces shall be designed to
effectively collect surface water and discharge to an outfall.
It shall have a minimum gradient of 0.5 percent and must be
paved with reinforced concrete not less than 75 mm in
thickness or an approved equal paving material.

A single run of swale or ditch shall not collect runoff from a
tributary area exceeding 1,000 m 2 (projected area) without
discharging into a down drain.

302.6.3 Subsurface Drainage

Cut and fill slopes shall be provided with surface drainage
as necessary for stability.

302.6.4 Disposal

All drainage facilities shall be designed to carry waters to
the nearest practicable drainage way approved by the
Building Official or other appropriate jurisdiction as a safe
place to deposit such waters. Erosion of ground in the area
of discharge shall be prevented by installation of non-
erosive down drains or other devices or splash blocks.

Building pads shall have a drainage gradient of 2 percent
toward approved drainage facilities, unless waived by the
Building Official.

Note:

The gradient from the building pad may be 1 percent if all
of the following conditions exist throughout the permit
area:

L No proposed fills are greater than 3 m in maximum
depth .

2. No proposed finish cut or fill slope faces have a
vertical height in excess of 3 m.

3. No existing slope faces steeper than 1 unit vertical in
10 units horizontal (10% slope) have a vertical height
in excess of 3m.

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CHAPTER 3 - Earthworks and Foundations 3-7

302.6.5 Interceptor Drains

Paved or Lined interceptor drains shall be installed along
the top of all cut slopes where the tributary drainage area
above slopes toward the cut has a drainage path greater than
12 m measured horizontally. Unless specified otherwise by
the Engineer of Record, interceptor drains shall be paved
with a minimum of 75 mm of concrete or gunite and
reinforced. They shall have a minimum depth of 300 mm
and a minimum paved width of 750 mm measured
horizontally across the drain. The slope of drain shall be
approved by the building official. Interceptor drains shall be
provided with outfalls spaced at regular intervals sufficient
enough to avoid overflow of drains. In cases where neither
reinforced concrete nor reinforced gunite shall be used as
the paving material for the drain, sufficient testing on the
alternative material must be conducted to determine its
effectiveness and durability as a channel lining material.

302.7 Erosion Control

302.7.1 Slopes

The faces of cut and fill slopes shall be prepared and
maintained to control against erosion. This erosion control
may consist of biotechnical or geosynthetic intervention
adapted to the local conditions. The protection for the
slopes shall be installed as soon as practicable and prior to
calling for final approval. Where cut slopes are not subject
to erosion due to the erosion-resistant character of the
materials, such protection may be omitted.

302.7.2 Other Devices

Where necessary, check dams, cribbing, riprap or other
devices or methods shall be employed to control erosion
and provide safety.

and biological attack, mechanical damage, creep,
installation damage and pH conditions to the reinforcement.

Select Granular Backfill shall consist of sound, durable,
granular material free from organic matter or other
deleterious material (such as shale or other soft particles
with poor durability).

The select granular backfill materials for these earth
structures shall conform to Grading Requirements as stated
in Table 302.1

Table 302-1 Grading Requirements

Standard Sieve

Percent by Mass Passing

Opening (mm)

Designated Sieve

(AASHTO T 27 and Til)

100

0.0425

0-60

0.075

0-15

The angle of internal friction for the backfill material shall
not be less than 34°.

The assigned cohesion value during the design stage for the
backfill material within the reinforced zone shall not exceed
5 kPa.

The soils should be compacted to no less than 95% MDD
determine according to AASHTO T 99 Method C or D and
corrected for oversized material according to AASHTO T
99, Note 9.

The material shall have a Plasticity Index of not more than
15 for rigid faced MSE structures, and not more than 20 for
flexible or ductile faced MSE structures, as determined by
AASHTO T 90.

302.7.2 Scour Protection

Retaining structures and foundations located on stream
banks and beds shall be provided with appropriate
countermeasures, designed on the basis of a detailed
engineering study, for long-term protection against scouring
and erosion.

302.8 MSE Structures and Similar Reinforced
Embankments and Fills

The design of Mechanically Stabilized Earth (MSE)
Structures and Similar Reinforced Embankments and Fills
shall incorporate provisions for internal and external
drainage.

The design for the required reinforcement shall take into
consideration the detrimental effects of corrosion, chemical

Electrochemical requirements for Mechanically Stabilized
Earth (MSE) retaining walls with metallic reinforcements
shall comply with summarized in Table 302-2.

Table 302-2 Electrochemical Requirements

Test

Requirements

Resistivity, AASHTO

T 288

pH, AASHTO T 289
Sulfate Content
AASHTO T 290
Chloride Content
AASHTO T 291

3000 Q-cm min.

5.0 to 10.0

200 ppm max.

1 00 ppm max.

Electrochemical requirements for Mechanically Stabilized
Earth MSE retaining walls with Geosynthetic

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3-8 CHAPTER 3 - Earthworks and Foundations

reinforcements specify that the pH shall be between 5.0 to
10.0 as determined by AASHTO T 289.

SECTION 303

FOUNDATION INVESTIGATION

303.1 General

Foundation investigation shall be conducted and a
Professional Report shall be submitted at each building site
For structures two storeys or higher, an exhaustive
geotechnical study shall be performed to evaluate in-situ
soil parameters for foundation design and analysis. The
minimum required number of boreholes per structure based
on footprint area is summarized in Table 303-1. All of these
boreholes should fall within the footprint of the structure,
and should generally be uniformly distributed throughout
the building footprint. Unless specified by the consulting
Geotechnical Engineer, all boreholes should be drilled to a
depth of at least five meters into hard strata or until a
suitable bearing layer is reached. For buildings with
basements, the depth of boring should extend to twice the
least dimension of the structure’s footprint (2B) added to
the depth of the basement.

Table 303-1 Minimum required number of boreholes per
structure.

FOOTPRINT AREA OF
STRUCTURE (m 2 )

MINIMUM REQUIRED
NUMBER OF
BOREHOLES*

A < 50

50 < A < 500

A >500

2 + (A/1000)**

(Rounded Up to Nearest
Integer)

*The minimum required number of boreholes should in no
way be construed as an upper limit value.

** “A” corresponds to the footprint area of the structure in

m .

An exhaustive geotechnical investigation should also be
conducted in cases of:

1) questionable soils, expansive soils, or problematic
soils (e.g. liquefiable, organic, compressible,
sensitive, etc.);

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-9

2) to determine whether the existing groundwater
table is above or within 1.5 meters below the
elevation of the lowest floor level;

3) where such floor is located below the finished
ground level adjacent to the foundation;

4) in cases where the use of pile foundations and/or
ground improvement are anticipated;

5) in areas underlain by rock strata where the rock is
suspected to be of questionable characteristics or
indicate variations in the structure of the rock or
where solution cavities or voids are expected to be
present in the rock; and

6) other cases deemed necessary by the Geotechnical
Engineer.

The Building Official may require that the interpretation
and evaluation of the results of the foundation investigation
be made by a geotechnical engineer,

303.2 Soil Classification

For the purposes of this chapter, the definition and
classification of soil materials for use in Table 304-1 shall
be according to ASTM D-2487.

Soil classification shall be based on observation and any
necessary tests of the materials disclosed by borings or
excavations made in appropriate locations. Additional
studies may be necessary to evaluate soil strength, the effect
of moisture variation on soil-bearing capacity,
compressibility, liquefaction susceptibility and expansion
potential.

303.3 Questionable Soils

Where the classification, strength or compressibility of the
soil are unknown, or where a load bearing value superior to
that specified in this code is claimed, the Building Official
shall require that these be verified through the necessary
geotechnical study stipulated in Section 303.1.

303.4 Liquefaction Study

A liquefaction susceptibility assessment in accordance with
accepted practice is warranted if both conditions below are
discovered during the course of the geotechnical
investigation:

1 . Shallow ground water, 2 m or less.

2, Unconsolidated saturated sandy alluvium (N < 15)

Exception:

The building official may waive this evaluation upon receipt
of written opinion of a qualified geotechnical engineer that
liquefaction is not probable.

303.5 Expansive Soils

Soils meeting all four of the following provisions shall be
considered expansive:

1. Plasticity index (PT) of 15 or greater, determined in
accordance with ASTM D 4318.

2. More than 10 percent of the soil particles pass a No.
200 sieve (75 m), determined in accordance with
ASTMD-422.

3. More than 10 percent of the soil particles are less than
5 micrometers in size, determined in accordance with
ASTM D-422.

4. Expansion index greater than 20, determined in
accordance with ASTM D-4829.

Tests that show compliance with Items 1, 2 and 3 shall not
be required if the test prescribed in Item 4 is conducted.

303.5.1 Design for Expansive Soils

Footings or foundations for buildings and structures
founded on expansive soils shall be designed in accordance
with Section 1805,8.1 or 1805.8.2.

Footing or foundation design need not comply with Section
303.5.3 or 303.5.4 where the soil is removed in accordance
with Section 303.5.4, nor where the building official
approves stabilization of the soil in accordance with Section
303.5.5.

303.5.2 Foundations

Footings or foundations placed on or within the active zone
of expansive soils shall be designed to resist differential
volume changes and to prevent structural damage to the
supported structure. Deflection and racking of the supported
shall be limited to that which will not interfere with the
usability and serviceability of the structure.

Foundations placed below where volume change occurs or
below expansive soil shall comply with the following
provisions:

1. Foundations extending into or penetrating expansive
soils shall be designed to prevent uplift of the
supported structure.

2. Foundations penetrating expansive soils shall be
designed to resist forces exerted on the foundation due

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3-10 CHAPTER 3 - Earthworks and Foundations

to soil volume changes or shall be isolated from the
expansive soil.

303.5.3 Slab-on-Ground, Foundations

Moments, shears and deflections for use in designing slab-
on-ground, mat or raft foundations on expansive soils shall
be determined in accordance with WR1/CRSI Design of
Slab-on-Ground Foundations or PTI Standard
Requirements for Analysis of Shallow Concrete
Foundations on Expansive Soils. Using the moments,
shears and deflections determined above, non-prestressed
slabs-on-ground, mat or raft foundations on expansive soils
shall be designed in accordance with PTI Standard
Requirements for Design of Shallow Post-Tensioned
Concrete Foundations on Expansive Soils. It shall be
permitted to analyze and design such slabs by other
methods that account for soil -structure interaction, the
deformed shape of the soil support, the place or stiffened
plate action of the slab as well as both center lift and edge
lift conditions. Such alternative methods shall be rational
and the basis for all aspects and parameters of the method
shall be available for peer review.

303.5.4 Removal of Expansive Soils

Where expansive soil is removed in lieu of designing
footings or foundations in accordance with Section 302.3.2,
the soil shall be removed to a depth sufficient to ensure a
constant moisture content in the remaining soil.
Fill material shall not contain expansive soils and shall
comply with Section 302.3.3.

Exception:

Expansive soil need not be removed to the depth of constant
moisture, provided the confining pressure in the expansive
soil created by the fill and supported structure exceeds the
swell pressure provided that the confining pressure
resulting from the fill and structural dead loads exceed the
swell pressure by 20%.

303.5.5 Stabilization

Where the active zone of expansive soils is stabilized in lieu
of designing footings or foundations in accordance with
Section 306.2, the soil shall be stabilized by chemical,
dewatering, pre-saturation or equivalent established
techniques.

303.6 Compressible Soils

If the borehole data show that the proposed structures are to
be built above compressible fine-grained soils (with N< 6 ),
it is recommended that consolidation tests be performed in
accordance with ASTM D 2435 to determine the settlement
parameters for the site.

If wide, massive loads within the structures to be built on
compressible fine-grained soils are to be expected for
prolonged periods of time, the settlement effects on existing
adjacent structures should be evaluated as well.

303.7 Reports

The soil classification and design-bearing capacity shall be
shown on the plans, unless the foundation conforms to
Table 305-1. The building official may require submission
of a written report of the investigation, which shall include,
but need not be limited to, the following information:

1 . A plot showing the location of all test borings,
surroundings and/or in-situ tests and excavations.

2. Technical descriptions and classifications of the
materials encountered.

3. Elevation of the water table, if encountered.

4. Recommendations for foundation type and design
criteria, including bearing capacity, provisions to
mitigate the effects of differential settlements and
expansive soils, provisions to mitigate the effects of
liquefaction and soil strength loss, provisions for
special foundation solutions, provisions for ground
improvement measures, and effects of loads on and due
to adjacent structures.

5. Expected total and differential settlement.

6. Laboratory test results of soil samples.

7. Field borehole log containing the following
information

a. Project location

b. Depth of borehole

c. Ground elevation

d. Ground water table elevation

e. Date started and finished

The soil classification and design-bearing capacity shall be
shown on the plans, unless the foundation conforms to
Table 305-1.

When expansive soils are present, the Building Official
may require that special provisions be made in the
foundation design and construction to safeguard against
damage due to this expansiveness. The building official
may require a special investigation and report to provide
these design and construction criteria.

303.8 Soil Tests

Tables 303-2 and 303-3 summarize the commonly used
field and laboratory tests needed in determining the in-situ

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-1 1

soil parameters for use in foundation design and analysis.

Table 303-3 Geophysical Tests

Table 303-2 Laboratory and Field Tests

Laboratory /
Field Test

ASTM/ Test
Designation

Output Data /
Parameter
Obtained

Classification of Soils

Moisture content

D22 16-05

Moisture/ water
content

Grain size
analysis

D422-63

Soil gradation

Atterberg Limits

D43 18-05

Liquid limit,
plastic limit

uses

D2487-00

Classification of
soils

Specific Gravity

D854-05

Specific gravity

Shrinkage Limit

D427-04

Shrinkage limit

Organic Matter

D2974-00

Moisture content,
ash content and
percent organic
matter in soil

Swedish Weight

Sounding Test

jis

A1221:2002

N sw - value
indicating,
undrained soil shear
strength

UCT Test (Soils)

D2 166-00

Strength

parameters

Tri-axial (UU
Test)

D2850-03a

Strength

parameters

Tri-axial (CU

Test)

D4767-04

Strength

parameters

Oedometer (1-D
Consolidation)

D2435-04

Consolidation

parameters

Laboratory Vane
Shear

D4648-05

Strength

parameters

Direct Shear

Test

D3080-04

Strength

parameters

UCT for Intact
Rock

D2938-95

Strength

parameters

Standard

Penetration Test

D1586-99

N- value

Modified Proctor
Test

D1557-02

Maximum dry
density

Standard Proctor

Test

D698-00a

Maximum dry
density

Field Density

Test

D1556-00

Maximum dry
density

CBR Lab Test

D1883-05

CBR

Cone Penetration
Test

D3441-05

Soil strength
parameters

Field Test

ASTM

Designation

Output Data /
Parameter
Obtained

Geophysical Tests

Seismic

refraction

D 5777-00

Maps subsurface
geologic conditions,
lithologic units and
fractures.

Seismic

refraction

D 7128

Map the top of
bedrock. Estimate
elastic wave velocity
of subsurface
materials.

Ground

Penetrating

Radar (GPR)

D 6432-11

Maps lateral
continuity of
lithologic units and
detects changes in
the acoustic
properties of
subsurface
geomaterials.

Crosshole
seismic survey

D 4428

p-wave and s-wave
velocity

determination, elastic
moduli determination

Downhole
seismic survey

D 7400

p-wave and s-wave
velocity
determination,
elastic moduli
determination

Geo-resistivity

Survey

D 6431-99

Determine
horizontal traveling
compression and
shear seismic
waves at test sites.

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3-12 CHAPTER 3 - Earthworks and Foundations

303.9 Liquefaction Potential and Soil Strength Loss

When required by Section 303.3, the potential for soil
liquefaction and soil strength loss during earthquakes shall
be evaluated during the geotechnical investigation. The
geotechnical evaluation shall assess potential consequences
of any liquefaction and soil strength loss, including
estimation of differential settlement, lateral movement or
reduction in foundation soil-bearing capacity, and discuss
mitigating measures. Such measures shall be given
consideration in the design of the building and may include,
but are not limited to: ground stabilization, selection of
appropriate foundation type and depths, selection of
appropriate structural systems to accommodate anticipated
displacements, or any combination of these measures.

The potential for liquefaction and soil strength loss shall be
evaluated for a site peak ground acceleration that, as a
minimum, conforms to the probability of exceedance
specified in Section 208.6.2. Peak ground acceleration may
be determined based on a site-specific study taking into
account soil amplification effects.

In the absence of such a study, peak ground acceleration
may be assumed equal to the seismic zone factor in'
Table 208-3.

303.10 Adjacent Loads

Where footings are placed at varying elevations, the effect
of adjacent loads shall be included in the foundation design.

303.11 Drainage

Provisions shall be made for the control and drainage of
surface water around buildings. (See also Section 305.5.5.)
and ensure that scour will not threaten such structures.

303.12 Plate Load Test

The plate load test is generally used for determination of
soil subgrade properties for rigid foundations. If used for
building foundations, it must be emphasized that the Depth
of Influence is only up to twice (2B) the width (B) of the
test plate. Care must be used when extending the results to
deeper depths as well as layered soils and variable
subsurface conditions.

SECTION 304

ALLOWABLE FOUNDATION AND
LATERAL PRESSURES

304.1 From Geotechnical Site Investigation and
Assessment

The recommended allowable foundation and lateral
pressures shall be estimated from a reasonably exhaustive
geotechnical site investigation and assessment, which shall
include at least the following:

a. Description of regional geologic characteristics;

b. Characterization of in-situ geotechnical conditions;

c. Factual report on the in-situ and laboratory tests
performed to characterize the site (See Section 303,7
for a list of in-situ and laboratory tests commonly
carried out for geotechnical site characterization);

d. Disclosure of the assumptions and the applicable
analytical or empirical models used in estimating the
allowable foundation and lateral pressures;

e. Calculations carried out and Factor of Safety (FS)
assumed in arriving at the recommended allowable
foundation and lateral pressures; and

f. Evaluation of existing potential geologic hazards and
those that may be induced or triggered by the
construction/installation of the structure.

The geotechnical site investigation and assessment shall be
performed by a geotechnical engineer.

A geotechnical investigation and assessment shall be
presented in a report. The report, together with a brief
resume and a sworn statement of accountability of the
geotechnical engineering consultant who prepared it, shall
be included in the submittals to be reviewed and examined
by the building official or government authority in charge
of issuing the relevant permits such as environmental
compliance certificate and/or building permit.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-13

304.2 Presumptive Load-Bearing and Lateral
^ Resisting Values

When no exhaustive geotechnical site assessment and
investigation is performed, especially when no in-situ or
very limited tests are carried out, the presumptive load-
bearing and lateral resisting values provided in Table 304-1
shall be used. Use of these values requires that the
foundation design engineer has, at the least, carried out an
inspection of the site and has become familiar with the
predominant soil or rock characteristics of the site.

Presumptive load-bearing values shall apply to materials
with similar physical characteristics and dispositions. Mud,
organic silt, organic clays, peat or unprepared fill shall not
be assumed to have a presumptive load-bearing capacity
unless data from a geotechnical site assessment and
investigation to substantiate the use of such a value are
submitted.

Table 304-1 Allowable Foundation and Lateral Pressure

Class of Materials 7

Allowable

Foundation

Pressure 2

(kPa)

Lateral
Bearing
Below Natural
Grade 5
(k Pa /m of
depth)

Lateral Sliding* 7

Coefficient 5

Resistance 6

(kPa)

1 . “Intact” Tuffaceous Sandstone a

1,000

300

2. “Lightly Weathered” Tuffaceous Sandstone b

500

150

3. Sandy Gravel and /or Gravel(GW & GP)

100

30 -

0.35

4. Well-graded Sand, Poorly-graded Sand, Silty Sand,
Clayey Sand, Silty Gravel and Clayey Gravel (SW,

SP, SM, SC, GM and GC)

0.25

5. Clay, Sandy Clay, Silty Clay and Clayey Silt (CL, ML,
MH, and CH)

50 c

1 A geotechnical site investigation is recommended for soil classification (Refer to Section 303).

All values of allowable foundation pressure are for footings having a minimum width of 300mm and a minimum depth of 300mm info the natural grade. Except as noted in
Footnote ‘a an increase of 20% is allowed for each additional 300mm of width and/or depth to a maximum value of three times the designated value . An increase of one-third
is permitted when using the alternate load combinations in Section 203,4 that include wind or earthquake loads

■* The resistance values derived from the table are permitted to be increased by the tabular value for each additional 300 mm of depth to a maximum of 15 times the tabular
value Isolated poles for uses such as flagpoles or signs and poles used to support buildings that are not adversely affected by a 12mm motion at (he ground surface due to
short-term lateral loads are permitted to be designed using lateral-bearing values equal to (wo times the tabular values ,

* Lateral bearing and sliding resistance may be combined.

* Coefficient to be multiplied by the dead load.

Lateral sliding resistance value to be multiplied by the contact area. In no case shall the lateral sliding resistance exceed one-half the dead load.
n Must satisfy both UCT mi „= 3Mpa and RQD >70
b Must satisfy both UCT mi „= IMpa and RQD >50
c No increase shall be allowed for an increase of width.

For clay, sandy clay, silty clay and clayey silt, in no case
shall the lateral sliding resistance exceed one-half the dead
load.

304.3 Minimum Allowable Pressures

The recommended allowable foundation and lateral values
shall be with the allowable stress design load combinations
specified in Section 203.4.

304.4 Foundations Adjacent to Existing
Retaining/Basement Walls

In cases where the adjacent building will have more
basements than the proposed building, the foundation of the
proposed building should be designed so as not to impart
additional lateral earth pressures on the existing building.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-14 CHAPTER 3 - Earthworks and Foundations

SECTION 305

footings

305.1 General

Footings and foundations shall be constructed of masonry,
concrete or treated wood in conformance with Chapters 4,
6 and 7. Footings of concrete and masonry shall be of
solid material. Foundations supporting wood shall extend
at least 150 mm above the adjacent finish grade. Footings
shall have a minimum depth as indicated in Table 305-1,
unless another depth is warranted, as established by a
foundation investigation.

The provisions of this section do not apply to building and
foundation systems in those areas subject to scour and
water pressure by wind and wave action. Buildings and
foundations subject to such loads shall be designed in
accordance with approved national standard

Table 305-1 Minimum Requirements for Foundations 1,2,3

Number of
Floors

Supported by
the Foundations

Thickness of
Foundation Wall
(mm)

Width

Footing

(mm)

Thickness

Footing

(mm)

Depth Below
Undisturbed
Ground
Surface (mm ) 4

Concrete

Unit

Masonry

150

300

150

300

200

375

175

450

250

450

200

600

1 Where unusual conditions are found, footings and foundations shall
be as required in Section 305. L

2 The ground under the floor may be excavated to the elevation of the
top of the footing.

3 Foundation may support a roof in addition to the stipulated number
of floors. Foundations supporting roofs only shall be as required for
supporting one floor.

305.2 Footing Design

Except for special provisions of Section 307 covering the
design of piles, all portions of footings shall be designed
in accordance with the structural provisions of this code
and shall be designed to minimize differential settlement
when necessary and the effects of expansive soils when
present.

Slab-on-grade and mat-type footings for buildings located
on expansive soils may be designed in accordance with
the geotechnical recommendation as permitted by the
building official.

305.2.1 Design Loads

Footings shall be designed for the most unfavorable load
effects due to combinations of loads. The dead load is
permitted to include the weight of foundations, footings
and overlying fill. Reduced live loads as permitted in the
Chapter on Loadings are permitted to be used in the
design of footings.

305.2.2 Vibratory Loads

Where machinery operations or other vibratory loads or
vibrations are transmitted to the foundations,
consideration shall be given in the Report to address the
foundation design to prevent detrimental disturbances to
the soil.

305.3 Bearing Walls

Bearing walls shall be supported on masonry or concrete
foundations or piles or other permitted foundation system
that shall be of sufficient size to support all loads.

Where a design is not provided, the minimum foundation
requirements for stud bearing walls shall be as set forth in
Table 305-1, unless expansive soils of a severity to cause
differential movement are known to exist.

Exceptions:

1. A one-story wood or metal-frame building not used
for human occupancy and not over 40 m 2 in floor
area may be constructed with walls supported on a
wood foundation plate permanently under the water
table when permitted by the building official

2. The support of buildings by posts embedded in earth
shall be designed as specified in Section 305. 7. Wood
posts or poles embedded in earth shall be pressure
treated with an approved preservative. Steel posts or
poles shall be protected as specified in Section
306.10.

305.4 Stepped Foundations

Foundations for all buildings where the surface of the
ground slopes more than 1 unit vertical in 10 units
horizontal (10% slope) shall be level or shall be stepped
so that both top and bottom of such foundation are level.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-15

Figure 305-1 Setback Dimensions for Building Clearance for Stable Natural Slopes on Firm and Intact Ground

305.5 Footings on or Adjacent to Slopes

305.5.1 Scope

The placement of buildings and structures on or adjacent
to slopes steeper than 1 unit vertical in 3 units horizontal
(33.3% slope) shall be in accordance with this section.

305.5.2 Building Clearance from Ascending Slopes

In general, buildings below slopes shall be set a sufficient
distance from the slope to provide protection from slope
drainage, erosion and shallow failures. Except as
provided for in Section 305.5.6 and Figure 305-1, the
following criteria will be assumed to provide this
protection. Where the existing slope is steeper than 1 unit
vertical in 1 unit horizontal (100% slope), the toe of the
slope shall be assumed to be at the intersection of a
horizontal plane drawn from the top of the foundation and
a plane drawn tangent to the slope at an angle of 45
degrees to the horizontal. Where a retaining wall is
constructed at the toe of the slope, the height of the slope
shall be measured from the top of the wall to the top of
the slope.

305.5.3 Footing Setback from Descending Slope
Surface

Footings on or adjacent to slope surfaces shall be founded
in firm material with an embedment and setback from the
slope surface sufficient to provide vertical and lateral
support for the footing without detrimental settlement.
Except as provided for in Section 305.5.6 and
Figure 305-1, the following setback is deemed adequate
to meet the criteria. Where the slope is steeper than 1 unit
vertical in 1 unit horizontal (100% slope), the required
setback shall be measured from an imaginary plane 45
degrees to the horizontal, projected upward from the toe
of the slope.

305.5.4 Pools

The setback between pools regulated by this code and
slopes shall be equal to one half the building footing
setback distance required by this section. That portion of
the pool wall within a horizontal distance of 2 meters
from the top of the slope shall be capable of supporting
the water in the pool without soil support.

305.5.5 Foundation Elevation

On graded sites, the top of any exterior foundation shall
extend above the elevation of the street gutter at point of
discharge or the inlet of an approved drainage device a
minimum of 300 mm plus 2 percent. The building official
may permit alternate elevations, provided it can be
demonstrated that required drainage to the point of
discharge and away from the structure is provided at all
locations on the site.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-16 CHAPTER 3 - Earthworks and Foundations

305.5.6 Alternate Setback and Clearance

305.7.2 Design Criteria

The Building Official may approve alternate setbacks and
clearances. The building official may require an
investigation and recommendation of a qualified engineer
to demonstrate that the intent of this section has been
satisfied. Such an investigation shall include
consideration of material, height of slope, slope gradient,
load intensity and erosion characteristics of slope
material.

305.5.7 Reinforced Slopes

Footings on or adjacent to slopes reinforced using rock
anchors, soils nails, geosynthethics or any other similar
ground improvement technique shall be founded such that
it does not interfere with or impair the function of the
reinforcing elements. The Building Official may require
the recommendation of a geotechnical engineer to
demonstrate that the reinforced slope can safely carry the
structural loads it will be subjected to.

305.6 Foundation Plates or Sills

Wood plates or sills shall be bolted to the foundation or
foundation wall. Steel bolts with a minimum nominal
diameter of 12 mm shall be used in Seismic Zone 2. Steel
bolts with a minimum nominal diameter of 16 mm shall
be used in Seismic Zone 4. Bolts shall be embedded at
least 180 mm into the concrete or masonry and shall be
spaced not more than 2 meters apart. There shall be a
minimum of two bolts per piece with one bolt located not
more than 300 mm or less than seven bolt diameters from
each end of the piece. A properly sized nut and washer
shall be tightened on each bolt to the plate. Foundation
plates and sills shall be the kind of wood specified in
Chapter 6.

305.7 Designs Employing Lateral Bearing

305.7.1 General

Construction employing posts or poles as columns
embedded in earth or embedded in concrete footings in
the earth may be used and designed to resist both axial
and lateral loads. The depth to resist lateral loads shall be
determined by means of the design criteria established
herein or other methods approved by the building official.

305.7.2.1 Non-constrained

The following formula may be used in determining the
depth of embedment required to resist lateral loads where
no constraint is provided at the ground surface, such as
rigid floor or rigid ground surface pavement.

(305-1)

where:

2.3 P

b = diameter of round post or footing or diagonal
dimension of square post or footing, m.
d = depth of embedment in earth in m but not over
3.5 m for purpose of computing lateral pressure,
m

fa = distance from ground surface to point of
application of P, m
p = applied lateral force, kN

S ± = allowable lateral soil-bearing pressure as set
forth in Table 304-1 based on a depth of one
third the depth of embedment, kPa
5 3 allowable lateral soil-bearing pressure as set
forth in Table 304-1 based on a depth equal to
the depth of embedment, kPa

305.7.2.2 Constrained

The following formula may be used to determine the
depth of embedment required to resist lateral loads where
constraint is provided at the ground surface, such as a
rigid floor or pavement.

7 Pk

dr = 4.25— (305-2)

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-17

305.7.2.3 Vertical load

y The resistance to vertical loads is determined by the
allowable soil-bearing pressure set forth in Table 304-1 .

305.7.3 Backfill

The backfill in the annular space around column not
embedded in poured footings shall be by one of the
following methods:

1 . Backfill shall be of concrete with an ultimate strength
of 15 MPa at 28 days. The hole shall not be less than
100 mm larger than the diameter of the column at its
bottom or 1 00 mm larger than the diagonal
dimension of a square or rectangular column.

2. Backfill shall be of clean sand. The sand shall be
thoroughly compacted by tamping in layers not more
than 200 mm in thickness.

305.7.4 Limitations

The design procedure outlined in this section shall be
subject to the following limitations:

305.7.4.1 The frictional resistance for retaining walls
and slabs on silts and clays shall be limited to one half of
the normal force imposed on the soil by the weight of the
footing or slab.

305.7.4.2 Posts embedded in earth shall not be used to
provide lateral support for structural or nonstructural
materials such as plaster, masonry or concrete unless
bracing is provided.

305.8 Grillage Footings

When grillage footings of structural steel shapes are used
on soils, they shall be completely embedded in concrete.
Concrete cover shall be at least 150 mm on the bottom
and at least 100 mm at all other points.

305.9 Bleacher Footings

Footings for open-air seating facilities shall comply with
Chapter 3 .

Exceptions:

Temporary open-air portable bleachers may be supported
upon wood sills or steel plates placed directly upon the
ground surface , provided soil pressure does not exceed
50 kPa.

SECTION 306

PILES-GENERAL REQUIREMENTS

306.1 General

Pile foundations shall be designed and installed on the
basis of a foundation investigation as defined in
Section 303 where required by the building official.

The investigation and report provisions of Section 303
shall be expanded to include, but not be limited to, the
following:

1. Recommended pile types and installed allowable
axial capacities, and estimated settlement.

2. Driving criteria.

3. Installation procedures.

4. Field inspection and reporting procedures (to include
procedures for verification of the installed bearing
capacity where required).

5. Pile load test requirements.

The use of piles not specifically mentioned in this chapter
shall be permitted, subject to the approval of the building
official upon submission of acceptable test data,
calculations or other information relating to the properties
and load-carrying capacities of such piles.

306.2 Interconnection

Individual pile caps- and caissons of every structure
subjected to seismic forces shall be interconnected by ties.
Such ties shall be capable of resisting, in tension or
compression, a minimum horizontal force equal to 10
percent of the largest column vertical load.

Exception:

Other approved methods may be used where it can be
demonstrated that equivalent restraint can be provided .

306.3 Determination of Allowable Loads

The allowable axial and lateral loads on piles shall be
determined by an approved formula, by a foundation
investigation or by load tests. Static axial compressive
pile load test shall be in accordance with ASTM Standard
D-1143, and lateral load testing of piles shall conform
with ASTM Standard D-3966. Dynamic pile tests shall
be in accordance with ASTM Standard D-4945. Static
axial tensile load testing to determine the uplift capacity
of pile-soil systems shall be in accordance with ASTM
Standard D-3689.

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3-18 CHAPTER 3 - Earthworks and Foundations

306.4 Static Load Test

Static axial compressive pile load test shall be in
accordance with ASTM Standard D-1143. The building
official may require that the test be conducted under the
supervision of a geotechnical engineer experienced and
knowledgeable in the practice of static pile load testing

When the allowable axial compressive load of a single
pile is determined by a static load test, one of the
following methods shall be used:

Method 1. It shall not exceed 50 percent of the yield
point under test load. The yield point shall be defined as
that point at which an increase in load produces a
disproportionate increase in settlement.

Method 2. It shall not exceed one half of the load, which
causes a net settlement, after deducting rebound, of

0.03 mm/kN of test load, which has been applied for a
period of at least 24 hours.

Method 3. It shall not exceed one half of that load under
which, during a 40-hour period of continuous load
application, no additional settlement takes place.

306.5 Dynamic Load Test

High-strain dynamic load test may be used to determine
the bearing capacity of piles, in accordance with
ASTM Standard D-4945. The building official may
require that the test be conducted by a geotechnical
engineer experienced and knowledgeable in the practice
of dynamic load testing.

306.6 Column Action

All piles standing unbraced in air, water or material not
capable of lateral support shall conform with the
applicable column formula as specified in this code. Such
piles driven into firm ground may be considered fixed and
laterally supported at 1.5 m below the ground surface and
in soft material at 3 m from the ground surface unless
otherwise prescribed by the building official after a
foundation investigation by an approved agency.

306.7 Group Action

Consideration shall be given to the reduction of allowable
pile load when piles are placed in groups.

Where soil conditions make such load reductions
advisable or necessary, the allowable axial and lateral
loads determined for a single pile shall be reduced by any
rational method or formula submitted to the building
official.

306.8 Lateral Loads

The design of piles subjected to lateral loads shall be
consistent with the design rules given Sections 306.1
through 306.7, where applicable. For foundations
involving piles subjected to lateral, the investigation and
report provisions of Section 303 shall be expanded to
include, but not be limited to:

1. Allowable lateral load capacity of recommended pile
type.

2. Resulting lateral displacements at allowable lateral
load.

3. Lateral pile load test requirements.

306.8.1 The design resistance of piles subjected to lateral
loads, should be assessed based on one of the following
failure mechanisms:

1 . For short piles, rotation or translation as a rigid body

2. For long slender piles, bending failure of the pile,
accompanied by local yielding and displacement of
the soil near the top of the pile.

306.8.2 Pile Groups

The group effects shall be considered when assessing the
resistance of laterally loaded pile groups.

306.8.3 Group interaction effects as well as head fixity
shall be accounted for when deriving the lateral resistance
of pile groups from results of load tests performed on
individual piles.

306.8.4 When assessing lateral load resistance from
results of subsurface investigation and pile strength
parameters, the transverse resistance of a pile or pile
group shall be calculated using a compatible set of
structural effects of actions, ground reactions and
displacements, and consider the possibility of structural
failure of the pile in the ground as well as the degree of
freedom of rotation of piles at the connection with the
structure.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-19

306.9 Piles in Subsiding Areas

^fVhere piles are driven through subsiding fills or other
subsiding strata and derive support from underlying
firmer materials, consideration shall be given to the
downward frictional forces, which may be imposed on the
piles by the subsiding upper strata.

Where the influence of subsiding fills is considered as
imposing loads on the pile, the allowable stresses
specified in this chapter may be increased if satisfactory
substantiating data are submitted.

306.10 Water Jetting

Installation of Piles by water shall not be used except
where and as specifically permitted by the building
official. When used, jetting shall be carried out in such a
manner that the carrying capacity of existing piles and
structures shall not be impaired. After withdrawal of the
jet, piles shall be driven down until the required resistance
is obtained.

306.10 Protection of Pile Materials

Where the boring records of site conditions indicate
possible deleterious action oh pile materials because of
soil constituents, changing water levels or other factors,
such materials shall be adequately protected by methods
or processes approved by the geotechnical engineer.

The effectiveness of such methods or processes for the
particular purpose shall have been thoroughly established
by satisfactory service records or other evidence, which
demonstrates the effectiveness of such protective
measures.

306.12 Allowable Loads

The allowable loads based on soil conditions shall be
established in accordance with Section 306,

Exception:

Any uncased cast-in-place pile may be assumed to
develop a frictional resistance equal to one sixth of the
bearing value of the soil material at minimum depth as set
forth in Table 305-1 but not to exceed 25 kPa unless a
greater value is allowed by the building official after a
foundation investigation as specified in Section 303 is
submitted Frictional resistance and bearing resistance
shall not be assumed to act simultaneously unless
recommended after a foundation investigation as
specified in Section 303.

306.13 Use of Higher Allowable Pile Stresses

Allowable compressive stresses greater than those
specified in Section 307 shall be permitted when
substantiating data justifying such higher stresses are
submitted to and approved by the building official. Such
substantiating data shall be included in the foundation
investigation report in accordance with Section 306. 1 .

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-20 CHAPTER 3 - Earthworks and Foundations

SECTION 307

#ILES-SPECIFIC REQUIREMENTS

307.1 Round Wood Piles

307.1.1 Material

Except where untreated piles are permitted, wood piles
shall be pressure treated. Untreated piles may be used
only when it has been established that the cutoff will be
below lowest groundwater level assumed to exist during
the life of the structure.

307.1.2 Allowable Stresses

The allowable unit stresses for round woodpiles shall not
exceed those set forth in Chapter 6.

The allowable values listed in, for compression parallel to
the grain at extreme fiber in bending are based on load
sharing as occurs in a pile cluster. For piles which
support their own specific load, a safety factor of 1.25
shall be applied to compression parallel to the grain
values and 1.30 to extreme fiber in bending values.

307.2 Uncased Cast-In-Place Concrete Piles
307.2.1 Material

Concrete piles cast in place against earth in drilled or
bored holes shall be made in such a manner as to ensure
the exclusion of any foreign matter and to secure a full-
sized shaft.

The length of such pile shall be limited to not more than
30 times the average diameter. Concrete shall have a
specified compressive strength f f c of not less than
17.5 MPa.

Exception:

The length of pile may exceed 30 times the diameter
provided the design and installation of the pile foundation
is in accordance with an approved foundation
investigation report

307.2.2 Allowable Stresses

The allowable compressive stress in the concrete shall not
exceed 0.33 f f c . The allowable compressive stress of
reinforcement shall not exceed 34 percent of the yield
strength of the steel or 175 MPa.

307.3 Metal-Cased Concrete Piles

307.3.1 Material

Concrete used in metal-cased concrete piles shall have a
specified compressive strength f r c of not less than
17.5 MPa.

307.3.2 Installation

Every metal casing for a concrete pile shall have a sealed
tip with a diameter of not less than 200 mm.

Concrete piles cast in place in metal shells shall have
shells driven for their full length in contact with the
surrounding soil and left permanently in place. The shells
shall be sufficiently strong to resist collapse and
sufficiently watertight to exclude water and foreign
material during the placing of concrete.

Piles shall be driven in such order and with such spacing
as to ensure against distortion of or injury to piles already
in place. No pile shall be driven within four and one-half
average pile diameters of a pile filled with concrete less
than 24 hours old unless approved by the geotechnical
engineer.

307.3.3 Allowable Stresses

Allowable stresses shall not exceed the values specified in
Section 307.2.2, except that the allowable concrete stress
may be increased to a maximum value of 0.40/^ for that
portion of the pile meeting the following conditions:

1. The thickness of the metal casing is not less than
1.7 mm (No. 14 carbon sheet steel gage).

2. The casing is seamless or is provided with seams of
equal strength and is of a configuration that will
provide confinement to the cast-in-place concrete.

3. The specified compressive strength f' c shall not
exceed 35 MPa and the ratio of steel minimum
specified yield strength F y to concrete specified
compressive strength f' c shall not be less than 6.

4. The pile diameter is not greater than 400 mm.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-21

307.4 Precast Concrete Piles

307.4.1 Materials

Precast concrete piles shall have a specified compressive
strength f f c of not less than 20 MPa, and shall develop a
compressive strength of not less than 20 MPa before
driving.

307.4.2 Reinforcement Ties

The longitudinal reinforcement in driven precast concrete
piles shall be laterally tied with steel ties or wire spirals.
Ties and spirals shall not be spaced more than 75 mm
apart, center to center, for a distance of 600 mm from the
ends and not more than 200 mm elsewhere. The gage of
ties and spirals shall be as follows:

1. For piles having a diameter of 400 mm or less, wire
shall not be smaller than 5.5 mm (No. 5 B.W.gage).

2. For piles, having a diameter of more than 400 mm
and less than 500 mm, wire shall not be smaller than
6 mm (No. 4 B.W.gage).

3. For piles having a diameter of 500 mm and larger,
wire shall not be smaller than 6.5 mm
(No. 3 B.W. gage).

307.4.3 Allowable Stresses

Precast concrete piling shall be designed to resist stresses
induced by handling and driving as well as by loads. The
allowable stresses shall not exceed the values specified in
Section 307.2.2.

307.5 Precast Prestressed Concrete Piles
(Pretensioned)

307.5.1 Materials

Precast prestressed concrete piles shall have a specified
compressive strength f r c of not less than 35 MPa and shall
develop a compressive strength of not less than 27 MPa
before driving.

307.5.2 Reinforcement

307.5.2.1 Longitudinal Reinforcement

The longitudinal reinforcement shall be high-tensile
seven-wire strand conforming to ASTM Standards.
Longitudinal reinforcement shall be laterally tied with
steel ties or wire spirals.

307.5.2.2 Transverse Reinforcement

Ties or spiral reinforcement shall not be spaced more than
75 mm apart, center to center, for a distance of 600 mm
from the ends and not more than 200 mm elsewhere.

At each end of the pile, the first five ties or spirals shall be
spaced 25 mm center to center.

For piles having a diameter of 600 mm or less, wire shall
not be smaller than 5.5 mm (No. 5 B.W.gage).

For piles having a diameter greater than 600 mm but less
than 900 mm, wire shall not be smaller than 6 mm
(No. 4 B.W.gage).

For piles having a diameter greater than 900 mm, wire
shall not be smaller than 6.5 mm (No. 3 B.W. gauge).

307.5.3 Allowable Stresses

Precast prestressed piling shall be designed to resist
stresses induced by handling and driving as well as by
loads. The effective prestress in the pile shall not be less
than 2.5 MPa for piles up to 10 m in length, 4 MPa for
piles up to 15 m in length, and 5 MPa for piles greater
than 1 5 meters in length.

The compressive stress in the concrete due to externally
applied load shall not exceed:

fc — 0 . 33/^ — 0 . 'll f p C (307-1)

where

f pc = effective prestress stress on the gross
section.

Effective prestress shall be based on an assumed loss of
200 MPa in the prestressing steel. The allowable stress in
the prestressing steel shall not exceed the values specified
in Section 418.6.

307.5.4 Splicing

Where required, splicing for concrete piles shall be by use
of embedded and properly anchored thick steel plates at
the ends being joined which shall then be fully welded, or
by use of adequate sized dowel rods and steel receiving
sleeves. The dowels and the faces shall then be joined by
structural epoxy. Metal splice cans are not allowed.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-22 CHAPTER 3 - Earthworks and Foundations

307.6 Structural Steel Piles
30f.6.1 Material

Structural steel piles, steel pipe piles and fully welded
steel piles fabricated from plates shall conform to one of
the material specifications listed in Section 501.3.

307.6.2 Allowable Stresses

The allowable axial stresses shall not exceed 0.35 of the
minimum specified yield strength F y or 85 MPa,
whichever is less.

Exception:

When justified in accordance with Section 306.12 , the
allowable axial stress may be increased above 85 MPa
and 0. 35 F y , but shall not exceed 0. 5 F y .

307.6.3 Minimum Dimensions

Sections of driven H-piles shall comply with the
following:

1. The flange projection shall not exceed 14 times the
minimum thickness of metal in either the flange or
the web, and the flange widths shall not be less than
80 percent of the depth of the section.

2. The nominal depth in the direction of the web shall
not be less than 200 mm.

3. Flanges and webs shall have a minimum nominal
thickness of 10 mm.

Sections of driven pipe piles shall have an outside
diameter of not less than 250 mm and a minimum
thickness of not less than 6 mm.

307.7 Concrete-Filled Steel Pipe Piles
307.7.1 Material

The steel pipe of concrete-filled steel pipe piles shall
conform to one of the material specifications listed in
Section 501.3. The concrete in concrete-filled steel pipe
piles shall have a specified compressive strength f f c of not
less than 17.5 MPa.

307.7.2 Allowable Stresses

The allowable axial stresses shall not exceed 0.35 of the
minimum specified yield strength F y of the steel or 0.33
of the specified compressive strength f f c of concrete,
provided F y shall not be assumed greater than 250 MPa
for computational purposes.

Exception:

When justified in accordance with Section 306.12, the
allowable stresses may be increased to 0. 50 F y .

307.7.3 Minimum Dimensions

Driven piles of uniform section shall have a nominal
outside diameter of not less than 200 mm.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-23

SECTION 308

FOUNDATION CONSTRUCTION-
SEISMIC ZONE 4

308.1 General

In Seismic Zones 4, the further requirements of this
section shall apply to the design and construction of
foundations, foundation components and the connection
of superstructure elements thereto. See Section 421.10
for additional requirements for structural concrete
foundations resisting seismic forces.

308.2 Foundation and Geotechnical Investigations

Where a structure is determined to be in Seismic Zone 4
in accordance with Section 208.4, an investigation shall
be conducted and shall include an evaluation of the
following potential hazards resulting from earthquake
motions: slope instability, liquefaction and surface rupture
due to faulting or lateral spreading.

In addition, the following investigations shall also be met:

1 . A determination of lateral pressures on basement and
retaining walls due to earthquake motions.

2. An assessment of potential consequences of any
liquefaction and soil strength loss, including
estimation of differential settlement, lateral
movement or reduction in foundation soil-bearing
capacity, and shall address mitigation measures. Such
measures shall be given consideration in the design
of the structure and can include but are not limited to
ground stabilization, selection of appropriate
foundation type and depths, selection of appropriate
structural systems to accommodate anticipated
displacements or any combination of these measures.
The potential for liquefaction and soil strength loss
shall be evaluated for site peak ground acceleration
magnitudes and source characteristics consistent with
the design earthquake ground motions. Peak ground
acceleration shall be determined from a site-specific
study taking into account soil amplification effects,
as specified in Section 208.4.

308.3 Footing Foundations

Where a structure is assigned to Seismic Zone 4 in
accordance with Section 208.4, individual spread footings
founded on soil defined in Section 208.4.3 as Soil profile
Type S E or S F shall be interconnected by ties. Ties shall
be capable of carrying, in tension or compression, unless
it is demonstrated that equivalent restraint is provided by
reinforced concrete beams within slabs on grade or
reinforced concretes labs on grade.

308.4 Pier and Pile Foundations

Where a structure is assigned to Seismic Zone 4 in
accordance with Section 208.4, the following shall apply.
Individual pile caps, piers or piles shall be interconnected
by ties. Ties shall be capable of carrying, in tension and
compression, unless it can be demonstrated that
equivalent restraint is provided by reinforced concrete
beams within slabs on grade, reinforced concrete slabs on
grade, confinement by competent rock, hard cohesive
soils or very dense granular soils. Concrete shall have a
specified compressive strength of not less than 3,000 psi
(20.68 MPa) at 28days.

Exception:

Piers supporting foundation walls , isolated interior posts
detailed so the pier is not subject to lateral loads , lightly
loaded exterior decks and patios and occupancy category
IV and V specified in Section 103 not exceeding two
stories of light-frame construction, are not subject to
interconnection if it can be shown the soils are of
adequate stiffness ; subject to the approval of the building
official.

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-24 CHAPTER 3 - Earthworks and Foundations

308.4.1 Connection to Pile Cap

For piles required to resist uplift forces or provide
rotational restraint, design of anchorage of piles into the
pile cap shall be provided considering the combined effect
of axial forces due to uplift and bending moments due to
fixity to the pile cap. Anchorage shall develop a minimum
of 25 percent of the strength of the pile in tension.
Anchorage into the pile cap shall be capable of
developing the following:

1 . In the case of uplift, the lesser of the nominal tensile
strength of the longitudinal reinforcement in a
concrete pile, or the nominal tensile strength of a
steel pile, or the pile uplift soil nominal strength
factored by 1.3 or the axial tension force resulting
from the load combinations of Section 203.

2. In the case of rotational restraint, the lesser of the
axial and shear forces, and moments resulting from
the load combinations of Section 203 or development
of the full axial, bending and shear nominal strength
of the pile.

308.4.2 Design Details for Piers, Piles and Grade
Beams

Piers or piles shall be designed and constructed to
withstand maximum imposed curvatures from earthquake
ground motions and structure response. Curvatures shall
include free-field soil strains modified for soil-pile-
structure interaction coupled with pier or pile
deformations induced by lateral pier or pile resistance to
structure seismic forces. Concrete piers or piles on soil
type S E or sites, as determined in Section 208.4.3,
shall be designed and detailed in accordance with
Sections 410 within seven pile diameters of the pile cap
and the interfaces of soft to medium stiff clay or
liquefiable strata. Grade beams shall be designed as
beams in accordance Section 4. When grade beams have
the capacity to resist the forces from the load
combinations in Section 203.

308.4.3 Flexural Strength

Where the vertical lateral-force-resisting elements are
columns, the grade beam or pile cap flexural strengths
shall exceed the column flexural strength. The connection
between batter piles and grade beams or pile caps shall be
designed to resist the nominal strength of the pile acting
as a short column. Batter piles and their connection shall
be capable of resisting forces and moments from the load
combinations of Section 203.

308.5 Driven Pile Foundations

308.5.1 Precast Concrete Piles

Where a structure is assigned to Seismic Zone 4, a
minimum longitudinal steel reinforcement ratio of 0.01
shall be provided for precast non-prestressed concrete
piles. The longitudinal reinforcing shall be confined with
closed ties or equivalent spirals of a minimum 3/8 in
(10 mm) diameter. Transverse confinement reinforcing
shall be provided at a maximum spacing of eight times the
diameter of the smallest longitudinal bar, but not to
exceed 6 in. (152 mm), within three pile diameters of the
bottom of the pile cap. Outside of the confinement region,
closed ties or equivalent spirals shall be provided at a 16
longitudinal-bar-diameter maximum spacing, but not
greater than 8 in. (200 mm). Reinforcement shall be full
length.

For Site Classes D through F, Transverse confinement
reinforcement consisting of closed ties or equivalent
spirals shall be provided in accordance with
Sections 2 1 .6.4.2 through 2 1 .6.4.4 of ACI 318 for the full
length of the pile.

In other than Site Classes E or F, the specified transverse
confinement reinforcement shall be provided within three
pile diameters below the bottom of the pile cap, but it is
permitted to use a transverse reinforcing ratio of not less
than one-half of that required in Section 21.6.4.4(a) of
ACI 3 1 8 throughout the remainder of the pile length.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 3 - Earthworks and Foundations 3-25

308.5.2 Precast Prestressed Piles

but not less than:

Wfiere a structure is assigned to Seismic Zone 4, the
following shall apply:

For the upper 20 ft (6 m) of precast prestressed piles, the
minimum volumetric ratio of spiral reinforcement shall
not be less than 0.007 or the amount required by the
following equation:

1 1.4 P

2 + 7?v

and need not exceed:

Ps = 0.021

where

(308.5.3)

(308.5.4)

Ps = 0. 12f' c /f yh (308.5.1)

where

fc = Specified compressive strength of

concrete, MPa

fyh = Yield strength of spiral reinforcement,

586 MPa

p s - Spiral reinforcement index

(volume spiral/volume of core)

A minimum of one-half of the volumetric ratio of spiral
reinforcement required by Eq. 308.5.1 shall be provided
for the remaining length of the pile.

Requirements of ACI 318, Chapter 2 1 , need not apply.

Where the total pile length in the soil is 35 It (10.668 mm)
or less, the lateral transverse reinforcement in the ductile
region shall occur through the length of the pile. Where
Ihe pile length exceeds 35 ft (10.668 mm), the ductile pile
region shall be taken as the greater of 3511 ( 1 0,668 mm) or
ihe distance from the underside of the pile cap to the point
of zero curvature plus three times the least pile
dimension.

In the ductile region, the center-to-center spacing of the
spirals or hoop reinforcement shall not exceed one-fifth
of the least pile dimension, six times the diameter of the
longitudinal strand, or 8 in (203 mm), whichever is
smaller.

Spiral reinforcement shall be spliced by lapping one full
turn, by welding, or by the use of a mechanical connector.
Where spiral reinforcement is lap spliced, the ends of the
spiral shall terminate in a seismic hook in accordance
with ACI 318, except that the bend shall be not less than
135°.

Where the transverse reinforcement consists of circular
spirals, the volumetric ratio of spiral transverse
reinforcement in the ductile region shall comply with the
following:

p s = 0.25 A

Jyk

1 1 . 4P

2 + 7Tv

(308.5.2)

A g - Pile cross-sectional area, mm 2

A c fi ~~ Core area defined by spiral outside diameter,
mm 2

f c ~ Specified compressive strength of concrete,

MPa <41.4 MPa

fyh - Yield strength of spiral reinforcement
<586 MPa

P — Axial load on pile resulting from the load
combination 1 2D + 0.5Z, + 1 .0 E, kN
Ps — Volumetric ratio (volume of spiral/ volume of
core)

This required amount of spiral reinforcement is permitted
to be obtained by providing an inner and outer spiral.

When transverse reinforcement consists of rectangular
hoops and cross ties, the total cross-sectional area of
lateral transverse reinforcement in the ductile region with

spacings, and perpendicular to dimension, h c , shall
conform to:

1.4

2 f c A

but not less than:

Aa = 0. 12 sh c Cp-

1 1.4 P

2 + 7^7j

l gJ

(308.5.5)

(308.5.6)

where

fyh

J ls/i

f'c

< 483 MPa

Cross-sectional dimension of pile core
measured center to center of hoop
reinforcement, mm

Spacing of transverse reinforcement
measured along length of pile, mm
Axial load, N

Cross-sectional area of transverse
reinforcement, mm 2
Gross area of pile, mm 2

Specified compressive strength of concrete,
MPa

National Structural Code of the Philippines Volume I, 7th Edition, 2015

3-26 CHAPTER 3 - Earthworks and Foundations

The hoops and cross ties shall be equivalent to deformed
bars not less than 10 mm in size. Rectangular hoop ends
shall terminate at a corner with seismic hooks.

Outside of the length of the pile requiring transverse
confinement reinforcing, the spiral or hoop reinforcing
with a volumetric ratio not less than one-half of that
required for transverse confinement reinforcing shall be
provided.

308.6 Cast-In-Place Concrete Foundations

Where a structure is assigned to Seismic Zone 4 a
minimum longitudinal reinforcement ratio of 0.005 shall
be provided for uncased cast-in-place drilled or augered
concrete piles, piers or caissons in the top one-half of the
pile length a minimum length of 10 feet (3,048 mm)
below ground or throughout the flexural length of the pile,
whichever length is greatest. The flexural length shall be
taken as the length of the pile to a point where the
concrete section cracking moment strength multiplied by
0.4 exceeds the required moment strength at that point.
There shall be a minimum of four longitudinal bars with
transverse confinement reinforcement provided in the pile
within three times the least pile dimension of the bottom
of the pile cap. A transverse spiral reinforcement ratio of
not less than one-half of that required in Section 410 for
other than Soil Profile Type S E , S F or as determined in
Section 208.4.3 or liquefiable sites is permitted. Tie
spacing throughout the remainder of the concrete section
shall neither exceed 12-longitudinal-bar diameters,
one-half the least dimension of the section, nor 12 inches
(305 mm). Ties shall be a minimum of 10mm bars for
piles with a least dimension up to 20 inches (508 mm),
and 12 mm bars for larger piles.

SECTION 309
SPECIAL FOUNDATION,

SLOPE STABILIZATION AND
MATERIALS OF CONSTRUCTION

309.1 Special Foundation Systems

Special foundation systems or materials other than
specified in the foregoing Sections may be introduced
provided that such systems can be supported by
calculations and theory to be providing safe foundation
systems and when approved by the Engineer of record.
Materials for incorporation into the foundation should
have proven track record of successful usage in similar
applications.

309.2 Acceptance and Approval

Structure support on improved ground using such special
systems or proprietary systems may be approved subject
to submittal of calculations and other proof of acceptance
and successful usage.

309.3 Specific Applications

Specialty foundation systems may be applied or used
specifically to address any or combinations of the
following: Bearing Capacity Improvement, Liquefaction
mitigation, slope stability enhancement, control and/or
acceleration of Consolidation settlements or immediate
settlements, increase in soil shear capacity, increased
pullout or overturniug capacity, special anchors in soil
and rock and other beneficial effects. Controlled low
strength materials (CLSM) to reduce fill loads may be
allowed for use where applicable.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

N8CP Cl 01-1 5

Chapter 4

STRUCTURAL CONCRETE

NATIONAL STRUCTURAL CODE OF THE PHILIPPINES
VOLUME I

BUILDINGS, TOWERS AND
OTHER VERTICAL STRUCTURES

SEVENTH EDITION, 2015

Association of Structural Engineers of the Philippines, Inc.
Suite 713, Future Point Plaza Condominium 1
112 Panay Avenue, Quezon City, Philippines 1100

Tel. No. : (+632) 410-0483
Fax No. : (+632) 411-8606
Email: aseponiine@gmail.com
Website: http:/Avww.aseponline.org

National Structural Code of the Philippines Volume I, 7th Edition, 2015

CHAPTER 4 - Structural Concrete 4-1

Table of Contents

SECTION 401. , ?

GENERAL REQUIREMENTS

401.1 Scope. . .. _ 7

401.2 General , ... ... 7

401.3 Purpose ... ..... . ....... ..... * 7

401.4 Applicability lfv w#; v; " 7

401.5 Interpretation.......,,. .. 8

401.6 Building Official .. g

401.7 Licensed Design Professional , . . g

401.8 Construction Documents and Design Records 9

401.9 Testing and Inspection ........ ...... 9

40 1 . 1 0 Approval of Special Systems of Design, Construction, or Alternative Construction Materials 9

401.11 Provisions for Earthquake Resistance ......... 9

SECTION 402 9

NOTATION AND TERMINOLOGY

402.1 Scope . ^ a 9

402.2 Notation . t 9

402.3 Terminology .. . .. ... 20

SECTION 403 w 28

REFERENCED STANDARDS 28

403.1 Scope 28

403.2 Referenced Standards 28

SECTION 404

STRUCTURAL SYSTEM REQUIREMENTS

404.1 Scope 3 ]

404.2 Materials ~ 31

404.3 Design Loads 31

404.4 Structural System and Load Paths 31

404.5 Structural Analysis 32

404.6 Strength . ....... 32

404.7 Serviceability ...... 32

404.8 Durability 32

404.9 Sustainability 33

404.10 Structural Integrity ... 33

404.1 1 Fire Resistance „ .. 33

404.12 Requirements for Specific Types of Construction ........... 33

404. 1 3 Construction and Inspection . 34

404.14 Strength Evaluation of Existing Structures 34

SECTION 405 34

LOADS „.34

405.1 Scope .*■*, ........... 34

405.2 General 34

405.3 Load Factors and Combinations 34

SECTION 406 . # 36

STRUCTURAL ANALYSIS * „ 36

National Structural Code of the Philippines Volume I, 7 th Edition, 2015

4-2

CHAPTER 4 - Structural Concrete

406.1 Scope * * * * *

£ 06.2 General * ■ * * **"■ *

406.3 Modeling Assumptions . •>**—■

406.4 Arrangement of Live Load - — — —

406.5 Simplified Method of Analysis for Non-Prestressed Continuous Beams and One-way Slabs

406.6 First-order Analysis

406.7 Elastic Second-order Analysis — - *

406.8 Inelastic Second-Order Analysis » *

406.9 Acceptability of Finite Element Analysis —

SECTION 407

37
37

38
41

,42

ONE-WAY SLABS

407.1 Scope *

407.2 General

407.3 Design Limits

407.4 Required Strength

407.5 Design Strength

407.6 Reinforcement Limits

407.7 Reinforcement Detailing,

SECTION 408

TWO-WAY SLABS

408.1 Scope

408.2 General

408.3 Design Limits

408.4 Required Strength. *

408.5 Design Strength

408.6 Reinforcement Limits

408.7 Reinforcement Detailing

408.8 Non-Prestressed Two-Way Joist Systems

408.9 Lift-slab Construction

408.10 Direct Design Method

408 . 1 1 Equivalent Frame Method

SECTION 409

.48

.51

.52

.56

.57

.60

.61

BEAMS

409.1 Scope

409.2 General

409.3 Design Limits *

409.4 Required Strength *

409.5 Design Strength *

409.6 Reinforcement Limits

409.7 Reinforcement Detailing..* *

409.8 Non-Prestressed One-way Joist Systems

409.9 Deep Beams —

SECTION 410

65
,68
69

.70

COLUMNS

410.1 Scope

410.2 General

410.3 Design Limits

410.4 Required Strength

410.5 Design Strength ,.*,****.

4 1 0.6 Reinforcement Limits

71
71

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 4 - Structural Concrete 4-3

410.7 Reinforcement Detailing ..... . ..... . — — * . ...71

SECTION 411 74

WALLS 74

411.1 Scope. ......... ..... . . ...... • ,«»> 74

41 1 .2 General . . ; * 74

411.3 Design Limits * v 74

41 1.4 Required Strength ..... ............ * < 75

41 1.5 Design Strength .. ■».*»..*. . 75

411.6 Reinforcement Limits.. 76

41 1 .7 Reinforcement Detailing . ........ ... 77

411.8 Alternative Method for Out-of-Plane Slender Wall Analysis * 78

SECTION 412 79

DIAPHRAGMS 79

412.1 Scope . 79

412.2 General > ■■■■■ 79

412.3 Design Limits ... 80

412.4 Required Strength 80

412.5 Design Strength * «. - . 80

412.6 Reinforcement Limits . 82

412.7 Reinforcement Detailing „ — 82

SECTION 413 83

FOUNDATIONS 83

413.1 Scope . .. * 83

413.2 General «, >. 83

413.3 Shallow Foundations ..... * * 84

413.4 Deep Foundations 85

SECTION 414 86

PLAIN CONCRETE 86

414.1 Scope 86

414.2 General . — 86

414.3 Design Limits . v ,.86

414.4 Required Strength . * * 87

414.5 Design Strength * 88

414.6 Reinforcement Detailing * * .. 89

SECTION 415 90

BEAM-CONCRETE AND 90

SLAB-COLUMN JOINTS 90

415.1 Scope - * * 90

415.2 General - 90

415.3 Transfer of Column Axial Force through the Floor System. 90

415.4 Detailing of Joints «. - 90

SECTION 416 91

CONNECTION BETWEEN MEMBERS 91

416.1 Scope 91

416.2 Connections of Precast Members. , ; * » 91

416.3 Connections to Foundations * . 92

416.4 Horizontal Shear Transfer in Composite Concrete Flexural Members * 94

National Structural Code of the Philippines Volume ! ; 7 lh Edition, 2015

4-4 CHAPTER 4 - Structural Concrete

416.5 Brackets and Corbels . . . — * - 95

SECTION 417 97

ANCHORING TO CONCRETE 97

417.1 Scope * * - 97

417.2 General * * ...... » *■ - — 98

417.3 General Requirements for Strength of Anchors * ... - 100

417.4 Design Requirements for Tensile Loading * ■* 102

417.5 Design Requirements for Shear Loading .. - — - 105

417.6 Interaction of Tensile and Shear Forces . - — ■ 108

417.7 Required Edge Distances, Spacings, and Thicknesses to Preclude Splitting Failure .. 108

417.8 Installation and Inspection of Anchors 109

SECTION 418 HO

EARTHQUAKE-RESISTANT STRUCTURES 110

418.1 Scope .«• v * 110

418.4 Intermediate Moment Frames * * * — 1 1 1

418.5 Intermediate Precast Structural Walls 113

418.6 Beams of Special Moment Frames *•,<■«■ * 1 13

418.7 Columns of Special Moment Frames — * — - 115

418.8 Joints of Special Moment Frames...... .....117

418.9 Special Moment Frames Constructed Using Precast Concrete... 119

418.10 Special Structural Walls - * * - - * — * 1 19

418.11 Special Structural Walls Constructed Using Precast Concrete . 123

418.12 Diaphragms and Trusses . 123

418.13 Foundations — ■■■■* 125

418.14 Members Not Designated as Part of the Seismic-Force-Resisting System* 127

SECTION 419 * * 128

CONCRETE: DESIGN AND DURABILITY REQUIREMENTS * * - 128

419.1 Scope * * 128

419.2 Concrete Design Properties >. 128

419.3 Concrete Durability Requirements -■■■- — * 129

419.3.1 Exposure Categories and Classes - * .129

419.4 Grout Durability Requirements . ....131

SECTION 420 131

STEEL REINFORCEMENT PROPERTIES, DURABILITY, AND EMBEDMENTS 131

420.1 Scope.. - « .. * — * 131

420.2 Non-Prestressed Bars and Wires .....131

420.3 Prestressing Strands, Wires, and Bars .................. **.<»...» ... 132

420.5 Headed Shear Stud Reinforcement... * 136

420.6 Provisions for Durability of Steel Reinforcement * - 1 36

420.7 Embedments * . 138

SECTION 421 139

STRENGTH REDUCTION FACTORS 139

421.1 Scope - * *-139

SECTION 422 142

SECTIONAL STRENGTH 142

422.1 Scope . - - * 142

422.2 Design Assumptions for Moment and Axial Strength ... 142

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 4 - Structural Concrete 4-5

422.3 Flexural Strength

422.4 Axial Strength or Combined Flexural and Axial Strength .

422.5 One-way Shear Strength

422.6 Two-Way Shear Strength

422.7 Torsional Strength

422.8 Bearing

422.9 Shear Friction

SECTION 423

. 143
. 143
,144
,147
, 150
,152
152

.154

STRUT-AND-TIE MODELS

423.1

423.2

423.3

423.4

423.5

423.6

423.7

423.8

423.9

Scope

General

Design Strength

Strength of Struts

Reinforcement Crossing Bottle-Shaped Struts

Strut Reinforcement Detailing

Strength of Ties

Tie Reinforcement Detailing

Strength of Nodal Zones

SECTION 424

157

SERVICEABILITY REQUIREMENTS

157

424.1

424.2

424.3

424.4

424.5

Scope...,. .

Deflections Due to Service-Level Gravity Loads

Distribution of Flexural Reinforcement in One-Way Slabs and Beams

Shrinkage and Temperature Reinforcement

Permissible Stresses in Prestressed Concrete Flexural Members

157

158

159

160

SECTION 425

161

REINFORCEMENT DETAILS 161

425.1 Scope ,, * 161

425 .2 Minimum Spacing of Reinforcement , j 6 1

425.3 Standard Hooks, Seismic Hooks, Crossties, and Minimum Inside Bend Diameters. .... 162

425.4 Development of Reinforcement ] 63

425.5 Splices * .. 167

425.6 Bundled Reinforcement * 169

425.7 Transverse Reinforcement 169

425.8 Post-Tensioning Anchorages and Couplers . 1 72

425.9 Anchorage Zones for Post-Tensioned Tendons 1 72

SECTION 426 175

CONSTRUCTION DOCUMENTS AND INSPECTION

..175

426.1

426.2

426.3

426.4

426.5

426.6

426.7

426.8

426.9

426.10

426.11

426.12

Scope „„

Design Criteria

Member Information

Concrete Materials and Mixture Requirements

Concrete Production and Construction

Reinforcement Materials and Construction Requirements

Anchoring to Concrete

Embedments

Additional Requirements for Precast Concrete

Additional Requirements for Prestressed Concrete

Formwork

Concrete Evaluation and Acceptance

National Structural Code of the Philippines Volume I, 7 tn Edition, 2015

CHAPTER 4 - Structural Concrete 4-5

422.3 Flexural Strength ... , _ _ __ 143

y 422.4 Axial Strength or Combined Flexural and Axial Strength ..... I 43

422.5 One-way Shear Strength 1 44

422.6 Two-Way Shear Strength . ,, ¥ ' 14 y

422.7 Torsional Strength . 250

422.8 Bearing . t v: " ^2

422.9 Shear Friction .... 2^2

SECTION 423 154

STRUT- AND-TIE MODELS 154

423.1 Scope * , 2^ 4

423.2 General ,,,, . _ . 2^4

423.3 Design Strength ,. _ 254

423.4 Strength of Struts _ 254

423.5 Reinforcement Crossing Bottle-Shaped Struts. . . 255

423.6 Strut Reinforcement Detailing . p 255

423.7 Strength of Ties 255

423.8 Tie Reinforcement Detailing * „„ pjr a 256

423.9 Strength of Nodal Zones...., ...... 256

SECTION 424

SERVICEABILITY REQUIREMENTS

424.1 Scope 157

424.2 Deflections Due to Service-Level Gravity Loads , ...... __ 157

424.3 Distribution of Flexural Reinforcement in One-Way Slabs and Beams.. „ 158

424.4 Shrinkage and Temperature Reinforcement 159

424.5 Permissible Stresses in Prestressed Concrete Flexural Members , 160

SECTION 425

REINFORCEMENT DETAILS

425.1 Scope .. ..... . . . 16 1

425.2 Minimum Spacing of Reinforcement K * 16 i

425.3 Standard Hooks, Seismic Hooks, Crossties, and Minimum Inside Bend Diameters 162

425.4 Development of Reinforcement . I 63

425.5 Splices . ..... . . , 16 7

425.6 Bundled Reinforcement „ t ,,.169

425.7 Transverse Reinforcement... . ^ I 69

425.8 Post-Tensioning Anchorages and Couplers _ 172

425.9 Anchorage Zones for Post-Tensioned Tendons 172

SECTION 426

CONSTRUCTION DOCUMENTS AND INSPECTION

426.1 Scope. f : ^. w# 175

426.2 Design Criteria . K iv . 175

426.3 Member Information 175

426.4 Concrete Materials and Mixture Requirements . 175

426.5 Concrete Production and Construction 178

426.6 Reinforcement Materials and Construction Requirements 181

426.7 Anchoring to Concrete .. 182

426.8 Embedments ; 182

426.9 Additional Requirements for Precast Concrete . 1 83

426.10 Additional Requirements for Prestressed Concrete 183

426.11 Formwork . 184

426. 12 Concrete Evaluation and Acceptance 1 85

National Structural Code of the Philippines Volume I, 7 th Edition, 2015

4-6

CHAPTER 4 - Structural Concrete

_ ...187

426.13 Inspection - " ' # 188

SECTION 427 1RR

STRENGTH EVALUATION OF EXISTING STRUCTURES ^ ^

427.1 Scope 188

427.2 General 188

427.3 Analytical Strength Evaluation ^ 189

427.4 Strength Evaluation by Load Test 1 90

427.5 Reduced Load Rating

SECTION 428

building code requirements for concrete thin shells w

1^1

428.1 Scope and Definitions - 191

428.2 Analysis and Design * * * "" 192

428.3 Design Strength * * . ..192

428 4 1 Cast-in-place Non-P restressed Concrete » - * 1 92

428.4.4 Specified Concrete Cover Requirements tor Corrosive Environm ■■■■■■ ] ^

428.5 Shell Reinforcement 194

428.6 Construction

SECTION 429 194

ALTERNATE DESIGN METHOD | ^

429.1 Notations 194

429.2 Scope 194

429.3 General 194

429.4 Permissible Service Load Stresses 1 95

429.5 Development and Splices of Reinforcement * 195

429.7 Compression Members With or Without Flexure " 195

429.8 Shear and Torsion

APPENDIX A 201

APPENDIX

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER4 - Structural Concrete 4-7

SECTION 401

/GENERAL REQUIREMENTS

401.1 Scope

401.1.1 This section addresses (a) to (h):

a. General requirements of this Chapter;

b. Purpose of this Chapter;

c. Applicability of this Chapter;

d. Interpretation of this Chapter;

e. Definition of building official and the licensed design
professional;

f. Construction documents;

g. Testing and inspection;

h. Approval of special systems of design, construction,
or alternative construction materials.

401.2 General

401.2.1 Chapter 4 refers to the structural concrete
provision of the National Structural Code of the
Philippines, Volume I (NSCP Vol. I), 7 th Edition and may
be cited as such, and will be referred to herein as “this
Code”.

401.2.2 This chapter provides minimum requirements
for the design and construction of structural concrete
elements of any building or other structure under
requirements of the National Building Code of the
Philippines of which this chapter of the National
Structural Code of the Philippines, Volume I, forms a
part. This chapter also covers the strength evaluation of
existing concrete structures.

For structural concrete, f f c shall not be less than 17 MPa.
No maximum value of f f c shall apply unless restricted by
a specific code provision.

401.2.3 This chapter is in English, with SI units,
published by the Association of Structural Engineers of
the Philippines, Inc.

401.2.4 In case of conflict between this edition and other
earlier versions, this latest version governs.

401.2.5 This chapter provides the minimum requirements
for the materials, design, construction, and strength
evaluation of structural concrete members and systems in
any structure designed and constructed under the
requirements of the general building code.

401.2.6 Modifications to this Code that are adopted by a
particular government agency or local government are
part of that organization’s requirements, but are not part
of this Code.

401.2.7 This chapter provides the minimum requirements
for the materials, design, construction* and strength
evaluation of structural concrete members and systems in
any structure within this Code.

401.3 Purpose

401.3.1 The purpose of this chapter is to provide for
public health and safety by establishing minimum
requirements for strength, stability, serviceability,
durability, and integrity of concrete structures.

401.3.2 This chapter does not address all design
considerations.

401.3.3 Construction means and methods are not
addressed in this section.

40 1 .4 Applicability

401.4.1 This chapter shall apply to concrete structures
designed and constructed under the requirements of the
general building code.'

401.4.2 Applicable provisions of this chapter shall be
permitted to be used for structures not governed by the
general building code.

401.4.3 The design of thin shells and folded plate
concrete structures shall be in accordance with Section
428.

401.4.4 Design and construction of structural concrete
slabs cast on stay-in-place, non-composite steel deck are
governed by this chapter.

401.4.5 Design and construction of one- and two-
family dwellings and multiple single-family dwellings
(townhouses) and their accessory structures may be
designed until such time provisions of the National
Structural Code of the Philippines, Volume III, Housing is
published.

National Structural Code of the Philippines Volume I, 7 th Edition, 2015

4-8 CHAPTER 4 - Structural Concrete

401.4.6 This chapter does not apply to the design and
installation of concrete piles, drilled piers, and caissons
embedded in ground except as provided in (a) or (b):

a. For portions in air or water, or in soil incapable of
providing adequate lateral restraint to prevent
buckling throughout their length. See also Sect.
418.13.1.2.

b. For structures in region of high seismic risk or
assigned to high seismic performance or design
categories

401.4.7 This chapter does not govern design and
construction of slabs-on-ground, unless the slab transmits
vertical loads or lateral forces from other portions of the
structure to the soil.

401.4.8 For unusual structures, such as arches, tanks,
reservoirs, bins and silos, blast-resistant structures, and
chimneys, provisions of this section shall govern where
applicable. For tanks and reservoirs refer also to ACI 350,
ACI 334. 1R, and ACI 372R.

40L4.9 This chapter does not govern the composite
design of structural concrete slabs cast-in-place,
composite steel form deck. Concrete used in the
construction of such slabs shall be governed by Sections
401 to 406 of this chapter, where applicable. Portions of
such slabs designed as reinforced concrete are governed
by this chapter.

401.5 Interpretation

401.5.1 The principles of interpretation in this Section
shall apply to this Chapter as a whole unless otherwise
stated.

401.5.2 This Chapter consists of sections and
appendices, including text, headings, tables, figures,
footnotes to tables and figures, and referenced standards.

401.5.3 This Chapter shall be interpreted in a manner
that avoids conflict between or among its provisions.
Specific provisions shall govern over general provisions.

401.5.4 This chapter shall be interpreted and applied in
accordance with the plain meaning of the words and terms
used. Specific definitions of words and terms in this
section shall be used where provided and applicable,
regardless of whether other materials, standards, or
resources outside of this section provide a different
definition.

401.5.5 The following words and terms in this section
shall be interpreted in accordance with (a) through (e):

a. The word “shall” is always mandatory;

b. Provisions of this section are mandatory even if the
word “shall” is not used;

c. Words used in the present tense shall include the
future;

d. The word “and” indicates that all of the connected
items, conditions, requirements, or events shall apply;

e. The word “or” indicates that all of the connected
items, conditions, requirements, or events are
alternatives, at least one of which shall be satisfied.

401.5.6 In any case in which one or more provisions of
this Chapter are declared by an appropriate court to be
invalid, that ruling shall not affect the validity of the
remaining provisions of this Chapter, which are severable.
The ruling of the court shall be effective only in that
court’s jurisdiction, and shall not affect the content of
interpretation of this Chapter in other jurisdictions.

401.5.7 If conflicts occur between provisions of this
code and standards and documents referenced in Section
403, this Chapter shall apply.

401.6 Building Official

401.6.1 All references in this chapter to the building
official shall be understood to mean the persons who
administer and enforce this Code.

401.6.2 Actions and decisions by the building official
affect only the specific jurisdiction and do not change this
Code.

401.6.3 The building official shall have the right to
order testing of any materials used in concrete
construction to determine if materials are of the quality
specified.

401.7 Licensed Design Professional

401.7.1 All references in this Code to the licensed design
professional shall be understood to mean the person who
is licensed and responsible for, and in charge of, the
structural design or inspection.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 4 - Structural Concrete 4-9

401.8 Construction Documents and Design Records

-401.8.1 The licensed design professional shall provide
in the construction documents the information required in
Section 426 and that required by the jurisdiction.

401.8.2 Calculations pertinent lo design shall be filed
with the construction documents if required by the
building official. Analyses and designs using computer
programs shall be permitted provided design assumptions,
user input, and computer-generated output are submitted.
Model analysis shall be permitted to supplement
calculations.

401.9 Testing and Inspection

401.9.1 Concrete materials shall be tested in
accordance with the requirements of Section 426.

401.9.2 Concrete construction shall be inspected in
accordance with the general building code and in
accordance with Sections 417 and 426.

401.9.3 Inspection records shall include information
required in Sections 417 and 426.

401.10 Approval of Special Systems of Design,
Construction, or Alternative Construction
Materials

401.10.1 Sponsors of any system of design,
construction, or alternative construction materials within
the scope oi this Chapter, the adequacy of which has been
shown by successful use or by analysis or test, but which
does not conform to or is not covered by this Chapter,
shall have the right lo present the data on which their
design is based to the building official or to a committee
of competent structural engineers appointed by the
building official. This committee shall have the authority
to investigate the data so submitted, require tests, and
formulate rules governing design and construction of such
systems to meet the intent of this Code. These rules, when
approved by the building official, and promulgated, shall
be of the same force and effect as the provisions of this
Code.

401.11 Provisions for Earthquake Resistance

401.11.1 In regions of moderate (seismic zone 2) or
high seismic risk (seismic zone 4), provisions of Section
418 shall be satisfied.

SECTION 402

NOTATION AND TERMINOLOGY

402.1 Scope

402.1.1 This section defines notation and terminology

used in this chapter.

402.2 Notation

a = shear span, distance between

concentrated load and face of
supports, mm.

a = depth of equivalent rectangular stress

block, mm.

ttp — shear span, equal to distance from

center of concentrated load to either:
(a) face of support for continuous or
cantilevered members, or (b) center
of support for simply supported
members, mm.

A = area of that part of cross section

between flexural tension face and
center of gravity of gross section,
mm 2 .

Ab = Area of an individual bar or wire,

mm 2 .

A brg = net bearing area of the head of stud,

anchor bolt, or headed deformed bar c

mm.

A c ~ area of concrete section resisting

shear transfer, mm 2 .

= area of contact surface being

investigated for horizontal shear,

mm .

A C f = greater gross cross-sectional area of

the slab-beam strips of the two
orthogonal equivalent frames
intersecting at a column of a two-way
slab, mm 2 .

A c h = cross-sectional area of a member

measured to the outside edges of
transverse reinforcement, mm 2 .

Acp = area enclosed by outside perimeter of

concrete cross section, mm 2 .

A C s = cross-sectional area at one end of a

strut in a strut-and-tie model, taken
perpendicular to the axis of the strut,
mm 2

A c t = area of that part of cross section

between the flexural tension face and
centroid of gross section, mm 2

National Structural Code of the Philippines Volume f 7 th Edition, 2015

4-1 0 CHAPTER 4 - Structural Concrete

= gross area of concrete section
bounded by web thickness and length
of section in the direction of shear
force considered in the case of walls,
and gross area of concrete section in
the case of diaphragms, not to exceed
the thickness times the width of the
diaphragm, mm 2 .

A cw = area 0 f concrete section of an

individual pier, horizontal wall
segment, or coupling beam resisting
shear, mm 2 .

Af = area of reinforcement in bracket or

corbel resisting design moment, mm 2

A g = gross area of concrete section, mm .

For a hollow section, A g is the area
of the concrete only and does not
include the area of the void(s).

A h = total area of shear reinforcement

parallel to primary tension
reinforcement in a corbel or bracket,
mm 2 .

Aj = effective cross-sectional area within a

joint in a plane parallel to plane of
beam reinforcement generating shear
in the joint, mm 2 .

A t = total area of longitudinal

reinforcement to resist torsion, mm .

A = minimum area of longitudinal

reinforcement to resist torsion, mm .

A n = area of reinforcement in bracket or

corbel resisting factored tensile force
Nuc> mm 2 .

A nz = area of a face of a nodal zone or a

section through a nodal zone, mm 2 .

A Na = projected influence area of a single

adhesive anchor or group of adhesive
anchors, for calculation of bond
strength intension, mm 2 .

A Nao = P r °j ecte( i influence area of a single

adhesive anchor, for calculation of
bond strength in tension if not limited
by edge distance or spacing, mm 2 .

A Nc = projected concrete failure area of a

single anchor or group of anchors,
for calculation of strength in tension,
mm 2 .

An co = projected concrete failure area of a

single anchor, for calculation of
strength intension if not limited by
edge distance or spacing, mm 2 .

A 0 = gross area enclosed by torsional shear

flow path, mm 2 .

A oh = area enclosed by centerline of the

outermost closed transverse torsional
reinforcement, mm 2 .

A p d = tot£ d area occupied by duct,

sheathing, and prestressing
reinforcement, mm 2 .

A ps = area of prestressed reinforcement in

tension zone, mm 2 .

A p t = total area of prestressing

reinforcement, mm 2 .

A s - area of non-prestressed longitudinal

tension reinforcement, mm 2 .

A! = area of compression reinforcement,

s 2
mm .

A sc = area of primary tension

reinforcement in a corbel or bracket,
mm 2 .

A S eN = effective cross-sectional area of

anchor intension, mm 2 .

A „ = effective cross-sectional area of

n se,V 2

anchor in shear, mm .

A S h = tota l cross-sectional area of

transverse reinforcement, including
crossties, within spacing s and

perpendicular to dimension b c , mm 2 .

A si = total area of surface reinforcement at

spacing s t in the i-th layer crossing a
strut, with reinforcement at an angle
a t to the axis of the strut, mm 2 .

A s min = minimum area of flexural
reinforcement, mm 2 .

A st = total area of non-prestressed

longitudinal reinforcement bars or
sfeel shapes, and excluding
prestressing reinforcement, mm .

A sx = area stee * s h a P e > piP e > or tu ^i n 8 m

a composite section, mm 2 .

A t = area of structural steel shape, pipe or

tubing in a composite section, mm .

A t = total area of longitudinal

reinforcement to resist torsion, mm .

A tp = area of prestressing reinforcement in

a tie, mm 2 .

A tr = total cross-sectional area of all

transverse reinforcement within
spacing s that crosses the potential
plane of splitting through the
reinforcement being developed,
mm 2 .

A ts = area of non-prestressed reinforcement

in a tie, mm.

A v = area of shear reinforcement within

spacing s, mm 2 .

A vd = total area of reinforcement in each

group of diagonal bars in a
diagonally reinforced coupling beam,

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 4 - Structural Concrete

4-1 1

mm 2 .

area of shear friction reinforcement,
mm 2 .

area of shear reinforcement parallel
to flexural tension reinforcement
within spacing s 2 , mm 2 ,
minimum area of shear reinforcement
within spacing s , mm 2 ,
projected concrete failure area of a
single anchor or group of anchors, for
calculation of strength in shear, mm 2 ,
projected concrete failure area of a
single anchor, for calculation of
strength in shear, if not limited by
comer influences, spacing, or
member thickness, mm 2 ,
loaded area for consideration of
bearing strength, mm 2 ,
maximum area of the portion of the
supporting surface that is
geometrically similar to and
concentric with the loaded area,
the area of the lower base of the
largest frustum of a pyramid, cone, or
tapered wedge contained wholly
within the support and having its
upper base equal to the loaded area.
The sides of the pyramid, cone, or
tapered wedge shall be sloped one
vertical to two horizontal, mm 2 ,
width of compression face of
member, mm.

cross-sectional dimension of member
core measured to the outside edges of
the transverse reinforcement
composing area A sh , mm.

Effective flange width of T section,
mm.

perimeter of critical section for two-

way shear in slabs and footings, mm.

width of a strut, mm.

the effective slab width resisting

Y f M sc .

width of that part of cross section

containing the closed stirrups

resisting torsion, mm.

width of cross section at contact

surface being investigated for

horizontal shear, mm.

web width or diameter of circular

section, mm.

dimension of the critical section b 0
measured in the direction of the span
for which moments are determined,
mm.

dimension of the critical section b 0

measured in the direction
perpendicular to b x , mm.

B n = nominal bearing strength, N.

B u = factored bearing load, N.

c — distance from extreme compression

fiber to neutral axis, mm.

c ac = critical edge distance required to

develop the basic strength as
controlled by concrete breakout or
bond of a post-installed anchor in
tension in uncracked concrete
without supplementary reinforcement
to control splitting, mm.

c a,max = maximum distance from center of an
anchor shaft to the edge of concrete,
mm.

c a,min = minimum distance from center of an

anchor shaft to the edge of concrete,
mm.

c al = distance from the center of an anchor

shaft to the edge of concrete in one
direction, mm. If shear is applied to
anchor, c al is taken in the direction
of the applied shear. If tension is
applied to the anchor, c al is the
minimum edge distance. Where
anchors subject to shear are located
in narrow sections of limited
thickness, See Section 417.5.2.4.

c' al = limiting value of c al where anchors

are located less than 1.5c al from
three or more edges, mm.

c a2 = distance from center of an anchor

'shaft to the edge of concrete in the
direction perpendicular to c al , mm.

c b = lesser of: (a) the distance from center

of a bar or wire to the nearest
concrete surface, and (b) one-half the
center-to-center spacing of bars or
wires being developed, mm.

c c = clear cover of reinforcement, mm.

c Na = projected distance from center of an

anchor shaft on one side of the
anchor required to develop the full
bond strength of a single adhesive
anchor, mm.

c t = distance from the interior face of the

column to the slab edge measured
parallel to c 1? but not exceeding c 1?
mm.

c x = dimension of rectangular or

equivalent rectangular column,

capital, or bracket measured in the
direction of the span for which
moments are being determined, mm.

c 2 = dimension of rectangular or

National Structural Code of the Philippines Voiume I, 7 th Edition, 2015

4-12 CHAPTER 4- Structural Concrete

equivalent rectangular column,
capital, or bracket measured in the
direction perpendicular to c l5 mm.

C = cross-sectional constant to define

torsional properties of slab and beam.
= compressive force acting on a nodal
zone, N.

C m = a factor relating actual moment

diagram to an equivalent uniform
moment diagram.

d = distance from extreme compression

fiber to centroid of longitudinal
tension reinforcement, mm.

d ' = distance from extreme compression

fiber to centroid of longitudinal
compression reinforcement, mm.

d a = outside diameter of anchor or shaft

diameter of headed stud, headed bolt,
or hooked bolt, mm.

d! a = value substituted for d a if an

oversized anchor is used, mm.

d a gg = Nominal maximum size of coarse

aggregate, mm.

d b = nominal diameter of bar, wire, or

prestressing strand, mm.

d p = distance from extreme compression

fiber to centroid of prestressed
reinforcement, mm.

dp He = diameter of pile at footing base, mm.

d s distance from extreme tension fiber

to centroid of tension reinforcement,
mm.

D = dead loads or related internal

moments and forces.

D = effect of service dead load.

e h = distance from the inner surface of the

shaft of a J- or L-bolt to the outer tip
of the J- or L-bolt, mm.

e N r distance between resultant tension

load on a group of anchors loaded in
tension and the centroid of the group
of anchors loaded in tension, mm;
e N t is always positive.

e v t = distance between resultant shear load

on a group of anchors loaded in shear
in the same direction, and the
centroid of the group of anchors
loaded in shear in the same direction,
mm; e v r is always positive.

= effect of horizontal and
earthquake-induced forces.

vertical

E c

= modulus of elasticity of
MPa.

concrete,

Ecb

= modulus of elasticity of beam
concrete, MPa.

Ecs

= modulus of elasticity

of slab

(£/)*,/

E p

E s

f'c

4Tc

fee

fei’

f cm
fet
fa

fdc

fpc

fpe

fps

concrete, MPa.

= flexural stiffness of member, N-mm 2 .

= Effective flexural stiffness of

member, N-mm 2 .

= modulus of elasticity of prestressing
reinforcement, MPa.

= modulus of elasticity of
reinforcement and structural steel,
excluding prestressing reinforcement,
MPa.

= specified compressive strength of
concrete, MPa.

= square root of specified compressive
strength of concrete, MPa.

= effective compressive strength of the
concrete in a strut or a nodal zone,
MPa.

= compressive strength of concrete at
time of initial prestress, MPa.

= square root of specified compressive
strength of concrete at time of initial
prestress, MPa.

= measured average compressive
strength of concrete, MPa.

= average splitting tensile strength of
lightweight concrete, MPa.

= stress due to unfactored dead load, at
extreme fiber of section where tensile
stress is caused by externally applied
loads, MPa.

= decompression stress; stress in the
prestressing steel when stress is zero
in the concrete at the same level as
the centroid of the prestressing steel,
MPa.

= compressive stress in concrete, after
allowance for all prestress losses, at
centroid of cross section resisting
externally applied loads or at junction
of web and flange where the centroid
lies within the flange, MPa. In a
composite member, f pc is resultant
compressive stress at centroid of
composite section, or at junction of
web and flange where the centroid
lies within the flange, due to both
prestress and moments resisted by
precast member acting alone.

= compressive stress in concrete due to
effective prestress forces, after
allowance for all prestress losses, at
extreme fiber of section if tensile
stress is caused by externally applied
loads, MPa.

= stress in prestressing steel at nominal
flexural strength, MPa.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

*n *»i

CHAPTER 4 - Structural Concrete 4-13

/pu

= specified tensile strength
prestressing reinforcement, MPa,

f py

= specified yield strength

prestressing reinforcement, MPa.

- modulus of rupture of concrete, MPa.

- tensile stress in reinforcement

service loads, excluding prestressing
reinforcement, MPa.

f s = compressive stress in reinforcement

under factored loads, excluding
prestressing reinforcement, MPa.

f se = effective stress in prestressed

reinforcement (after allowance for all
prestress losses), MPa.

f si = stress in the Ath layer of surface

reinforcement MPa.

ft = extreme fiber stress in tension in the

pre-compressed tensile zone
calculated at service loads using
gross section properties after
allowance of all prestress losses,
MPa.

futa = specified tensile strength of anchor

steel, MPa.

f y = specified yield strength of non-

prestressed reinforcement, MPa.

fya = specified yield strength of anchor

steel, MPa.

f yt = specified yield strength of transverse

reinforcement, MPa.

F = effect of service lateral load due to

fluids with well-defined pressures
and maximum heights.

F nn = nominal strength at face of a nodal

zone, N.

= nominal strength of a strut, N.

= nominal strength of a tie, N.

= factored force on the face of a node,
N.

F us = factored compressive force in a strut,

F ut = factored tensile force in a tie, N.

h = overall thickness of member, mm.

h = thickness of shell or folded plate,

mm.

h a = thickness of member in which an

anchor is located, measured parallel
to anchor axis, mm.

h>anc = dimension of anchorage device or

single group of closely spaced
devices in the direction of bursting
being considered, mm.

h e f = effective embedment depth of anchor,

mm.

h' e f = limiting value of h e f where anchors

are located less than l.Sh e f from

three or more edges, mm.
h sx = storey height for storey x,

h u = laterally unsupported height at

extreme compression of wall or wall
pier, mm., equivalent to F u for
compression members, mm.
h v = depth of shear head cross section,

h x

k c

k C p

k f

k, n

K t

K tr

*05

€

= height of entire wall from base to top,
or clear height of wall segment or
wall pier considered, mm.

= maximum center to center horizontal
spacing of hoop or crosstie legs on all
faces of the column, mm.

= effect of service load due to lateral
earth pressure, ground water
pressure, or pressure of bulk
materials, N.

= moment of inertia of section of beam
about the centroidal axis, mm 4 .

= moment of inertia about centroidal
axis of gross section of beam, mm 4 .

= moment of inertia of cracked section
transformed to concrete, mm 4 .

= effective moment of inertia for
computation of deflection, mm 4 .

= moment of inertia of gross concrete
section about centroidal axis,
neglecting reinforcement, mm 4 .

= moment of inertia about of slab about
centroidal axis, mm 4 .

= moment of inertia of reinforcement
about centroidal axis of member
- cross section, mm 4 .

= moment of inertia of structural steel
shape, pipe or tubing about centroidal
axis of composite member cross
section, mm 4 .

= effective length factor for
compression members.

= coefficient for basic concrete
breakout strength in tension.

= coefficient for pry out strength.

= concrete strength factor.

= confinement effectiveness factor.

= wobble friction coefficient per mm of
prestressing tendon.

= torsional stiffness of torsional
member; moment per unit rotation.

= transverse reinforcement index, mm.

= coefficient associated with the 5%
fractile.

= span length of beam or one-way slab;

clear projection of cantilever, mm.

= additional embedment length beyond
centerline of support or point of

National Structural Code of the Philippines Volume ! : 7 th Edition, 2015

4-14 CHAPTER 4 - Structural Concrete

inflection, mm.

£ = length along which anchorage of a tie

must occur, mm.

£ b = width of bearing, mm.

£ c = length of a compression member in a

frame, measured center-to-center of
the joints, mm.

£ d = development length in tension of

deformed bar, deformed wire, plain
and deformed welded wire
reinforcement, or pretensioned
strand, mm.

£ dc = development length in compression

of deformed bars and deformed wire,
mm.

£ dh = development length in tension of

deformed bar or deformed wire with
a standard hook, measured from
outside end of hook, point of

tangency, toward critical section,
mm.

£ e = load bearing length of anchor for

shear, mm.

£ n = length of clear span measured face-

to-face of supports, mm.

£ o = length, measured from joint face

along axis of member, over which
special transverse reinforcement must
be provided, mm.

£ sc = compression lap splice length, mm.

£ st = tension lap splice length, mm.

£ t = span of member under load test,

taken as the shorter span for two-way
slab systems, mm. Span is the lesser
of: (a) distance between centers of
supports, and (b) clear distance
between supports plus thickness h of
member. Span for a cantilever shall
be taken as twice the distance from
the face of support to cantilever end.

£ tr = transfer length of prestressed

reinforcement, mm.

£ u = unsupported length of column or

wall, mm

£ v = length of shear head arm from

centroid of concentrated load or
reaction, mm.

£ w = length of entire wall, or length of

wall segment or wall pier considered
in direction of shear force, mm.

£ x = length of prestressing tendon element

from jacking end to any point x , mm.

£ 1 = length of span in direction that

moments are being determined,
measured center-to-center of
supports, mm.

£ 2 = length of span in direction

perpendicular to £ l9 measured center-
to-center of supports, mm.

L = effect of service live load.

l d = development length, mm.

I = effect of service roof live load.

M = design moment

= maximum unfactored moment due to
service loads, including effects.

yif = moment acting on anchor or anchor

group, N-mm.

M a = maximum moment in member due to

service loads at stage deflection is
calculated, N-mm.

M c = moment at the face of the joint,

corresponding to the nominal flexural
strength of the column framing into
that joint, calculated for the factored
axial force, consistent with the
direction of the lateral forces
considered, resulting in the lowest
flexural strength.

M c = factored moment amplified for the

effects of member curvature used for
design of compression member, N-
mm.

M cr = cracking moment, N-mm.

M cre = moment causing flexural cracking at

section due to externally applied
loads, N-mm

M g - moment at the face of the joint,

corresponding to the nominal flexural
strength of the girder including slab
where in tension, framing into that
joint

M = factored moment modified to account

111 XT

for effect of axial compression, N-
mm.

M max = maximum factored moment at section
due to externally applied loads, N-
mm.

M n = nominal flexural strength at section,

N-mm.

M nb = nominal flexural strength of beam

including slab where in tension,
framing into joint, N-mm.

M nc = nominal flexural strength of column

framing into j oint, calculated for
factored axial force, consistent with
the direction of lateral forces
considered, resulting in lowest
flexural strength, N-mm.

M 0 = total factored static moment, N-mm.

M p = required plastic moment strength of

shearhead cross section, N-mm.

M pr = probable flexural strength of

Association of Structural Engineers of the Philippines, Inc. (ASEP)

members, with or without axial load,
determined using the properties of the
member at the joint faces assuming a

- modular ratio of elasticity, but not
less than 6

= e s /e c

tensile strength in the longitudinal
bars of at least 1.25 f y and a
strength-reduction factor (f> of 1.0, N-

= number of items, such as, bars, wires,
monostrand anchorage devices,
anchors or shearhead arms.

mm.

maximum moment in wall due to
service loads, excluding P A effects,
N-mm.

factored slab moment that is resisted
by the column at a joint, N-mm.

= number of longitudinal bars around
the perimeter of a column core with
rectilinear hoops that are laterally
supported by the corner of hoops or
by seismic hooks. A bundle of bars
is counted as a single bar.

portion of slab factored moment
balanced by support moment, N-mm
factored moment at section, N-mm.
moment at the mid-height section of
the wall due to factored lateral and
eccentric vertical loads, not including

P A effects, N-mm.

moment resistance contributed by
shearhead reinforcement, N-mm.

= design axial load normal to cross
section occurring simultaneously
with V; to be taken as positive for
compression, negative for tension,
and to include effects of tension due
to creep and shrinkage.

= number of bars in a layer being
spliced or developed at a critical
section.

lesser factored end moment on a
compression member, to be taken as

= tension force acting on anchor or
anchor group, N.

positive if member is bent in single
curvature, negative if bent in double

N a

= nominal bond strength intension of a
single adhesive anchor, N.

curvature, N-mm.

factored end moment on a

N ag

= nominal bond strength intension of a
group of adhesive anchors, N.

compression member at the end at
which M 1 acts, due to loads that
cause no appreciable sidesway,

N b

= basic concrete breakout strength in
tension of a single anchor in cracked
concrete, N.

calculated using a first-order elastic
frame analysis, N-mm.

N ba

= Basic bond strength in tension of a
single adhesive anchor, N.

factored end moment on compression
member at the end at which M x acts,
due to loads that cause appreciable
sidesway, calculated using a first-
order elastic frame analysis, N-mm.
greater factored end moment on

N c

= the resultant tensile force acting on
the portion of the concrete cross
section that is subjected to tensile
stresses due to the combined effects
of service loads and effective
prestress, N.

compression member. If transverse
loading occurs between supports,

N cb

= nominal concrete breakout strength in
tension of a single anchor, N.

M 2 is taken as the largest moment
occurring in member. Value of M 2

N cb g

= nominal concrete breakout strength in
tension of a group of anchors, N,

is always positive, N-mm.
minimum value of ilf 2 , N-mm.

N cp

= basic concrete pryout strength of a
single anchor, N.

factored end moment on compression
member at the end at which M 2 acts.

N C pg

= basic concrete pryout strength of a
group of anchors, N.

due to loads that cause no appreciable

= nominal strength in tension, N.

sidesway, calculated using a first-
order elastic frame analysis, N-mm.

N v

= pullout strength in tension of a single
anchor in cracked concrete, N.

factored end moment on compression
member at the end at which M 2 acts,

N pn

= nominal pullout strength in tension of
a single anchor, N

due to loads that cause appreciable
sidesway, calculated using a first-
order elastic frame analysis, N-mm.

N sa

= nominal strength of a single anchor
or individual anchors in a group of
anchors in tension as governed by the
steel strength, N.

4-1 6 CHAPTER 4 - Structural Concrete

N sb

N sbg

N u

N u a

^ua, g

Nua,i

ua,s

N„ r

Pep

,max

Pnt

nt, max

Ppi

P pu
Ppx

= side-face blowout strength of a single
anchor, N.

= side-face blowout strength of a group
of anchors, N.

= factored axial force normal to cross
section occurring simultaneously
with V u or T u \ to be taken as
positive for compression and
negative for tension, N.

= factored tensile force applied to
anchor or individual anchor in a
group of anchors, N.

= total factored tensile force applied to
anchor group, N.

= factored tensile force applied to most
highly stressed anchor in a group of
anchors, N.

= . Factored sustained tension load, N.

= factored horizontal tensile force
applied at top of bracket or corbel
acting simultaneously with V u ; to be
taken as positive for tension, N.

= outside perimeter of the concrete
cross section, mm.

= perimeter of centerline of outermost
closed transverse torsional
reinforcement, mm.

= critical buckling load, N.

= nominal axial compressive strength
of a member, N.

= maximum nominal axial compressive
strength of member, N.

= nominal axial tensile strength of
member, N.

= Maximum nominal axial tensile
strength of member, N.

= nominal axial load strength at zero
eccentricity, N.

= prestressing force at jacking end, N.

= factored prestressing force at
anchorage device, N.

= prestressing force evaluated at
distance £ px from the jacking end, N
= prestressing tendon force at jacking
end.

= unfactored axial load at the design,
mid-height section including effects
of self-weight, N.

= factored post-tensioned tendon force
at the anchorage device.

= factored axial load at given
eccentricity, < 4>Pn

= Factored axial force; to be taken as
positive for compression and
negative for tension, N.

P x

Qdu

Rlu

S s

s w

S 2

S e

= secondary moment due to individual
member slenderness, N-mm.

= secondary moment due to lateral
deflection, N-mm.

= prestressing tendon force at any point
x .

= factored dead load per unit area, kPa.

= factored live load per unit area, kPa.

= factored load per unit area, kPa.

= stability index for a storey.

= radius of gyration of cross section of
a compression member, mm.

= reaction, N.

= cumulative load effect of service rain
load.

= spacing of shear reinforcement in
direction parallel to longitudinal
reinforcement, mm.

= center-to-center spacing of items,
such as longitudinal reinforcement,
transverse reinforcement, tendons, or
anchors, mm.

= Standard deviation, MPa.

= center-to-center spacing of
reinforcements in the i-th layer
adjacent to the surface of the
member, mm.

= center-to-center spacing of transverse
reinforcements within the length
f 0 , mm.

= sample standard deviation, MPa.

= spacing of wire to be developed or
spliced, mm.

= clear distance between adjacent webs,
mm.

= center-to-center spacing of
longitudinal shear or torsional
reinforcement, mm.

= elastic section modulus of section.

= moment, shear or axial force at
connection corresponding to

development of probable strength at
intended yield locations, based on the
governing mechanism of inelastic
lateral deformation, considering both
gravity and earthquake load effects.

= elastic section modulus, mm 3 .

= nominal moment, shear, axial,
torsional, or bearing strength.

= yield strength of connection, based
on / y , for moment, shear, of axial
force, MPa.

= wall thickness of hollow section, mm.
= thickness of flange, mm.

Association of Structural Engineers of the Philippines ! Inc. (ASEP)

CHAPTER 4 - Structural Concrete 4-1 7

cumulative effects of service
temperature, creep, shrinkage,
differential settlement, and shrinkage
compensating concrete,
tension force acting on a nodal zone
in a strut-and-tie model, N.
cracking torsional moment, N-mm.
total test load, N.

threshold torsional moment, N-mm.
factored torsional moment at section,
N-mm.

strength of a member or cross section
required to resist factored loads or
related internal moments and forces
in such combinations as stipulated in
this Code.

design shear stress, MPa,

Stress corresponding to nominal two-
way shear strength provided by
concrete, MPa.

equivalent concrete stress
corresponding to nominal two-way
shear strength of slab or footing,
MPa.

equivalent concrete stress
corresponding to nominal two-way
shear strength provided by
reinforcement, MPa.

Maximum factored two-way shear
stress calculated around the perimeter
of a given critical section, MPa.
factored shear stress on the slab
critical section for two-way action
due to gravity loads without moment
transfer, MPa.

design shear force at section

shear force acting on anchor or

anchor group, N.

applied shear perpendicular to the
edge, N.

applied shear parallel to the edge, N.
basic concrete breakout strength in
shear of a single anchor in cracked
concrete, N.

nominal shear strength provided by
concrete, N.

nominal concrete breakout strength in
shear of a single anchor, N.
nominal concrete breakout strength in
shear of a group of anchors, N.
nominal shear strength provided by
concrete where diagonal cracking
results from combined shear and
moment, N.

nominal concrete pryout strength of a
single anchor, N.

v cpg

v cw

V d

V e

v h

V n

Vnh

V P

V s

v ua,g

v ua,i

v uh

W t

Wt,max

w/cm

W a

= nominal concrete pryout strength of a
group of anchors, N.

= nominal shear strength provided by
concrete where diagonal cracking
results from high principal tensile
stress in web, N.

= shear force at section due to
unfactored dead load, N.

= Design shear force for load
combinations including earthquake
effects, N.

= permissible horizontal shear stress,
MPa.

= factored shear force at section due to
externally applied loads occurring
simultaneously with M max , N.

= nominal shear strength, N.

= nominal horizontal shear strength, N.
= vertical component of effective
prestress force at section, N.

= nominal shear strength provided by
shear reinforcement, N.

= nominal strength in shear of a single
anchor or group of anchors as
governed by the steel strength, N.

= factored shear force at section, N.

= factored shear force applied to a
single anchor or group of anchors, N.
= total factored shear force applied to
anchor group, N.

= factored shear force applied to most
highly stressed anchor in a group of
anchors, N.

= Factored shear force along horizontal
interface in composite concrete
flexural member, N.

= factored horizontal shear in a storey,
N.

= density, unit weight, of normal-
weight concrete or equilibrium
density of lightweight concrete, kg/
m 3 .

= factored live load per unit area.

= factored load per unit length of beam
or one-way slab, N/mm.

= width of a strut perpendicular to the
axis of the strut, mm.

= effective height of concrete
concentric with a tie, used to
dimension nodal zone, mm.

= maximum effective height of
concrete concentric with a tie, mm.

= maximum water-cementitious
materials ratio.

= effect of wind load.

= service-level wind load, N.

National Structural Code of the Philippines Volume I, 7 th Edition, 2015

4-18 CHAPTER 4 - Structural Concrete

= shorter overall dimension of

Pds

—

rectangular part of cross section, mm.

= longer overall dimension of

rectangular part of cross section, mm.

= distance from centroidal axis of gross
section, neglecting reinforcement, to

Pdns

tension face, mm.

= angle between inclined stirrups and
longitudinal axis of member.

= angle defining the orientation of
reinforcement.

= total angular change of prestressing
tendon profile in radians from tendon

«c

a f

jacking end to any point x .

= coefficient defining the relative
contribution of concrete strength to
nominal wall shear strength
= ratio of flexural stiffness of beam

section to flexural stiffness of a width
of slab bounded laterally by
centerlines of adjacent panels, if any,
on each side of the beam.

a f

Ecb^b

F I

1j cs 1 s

Ctfm

= average value of af for all beams
on edges of a panel.

af 1 = ctf in direction of

- af in direction of

= angle between the axis of a strut and

—

the bars in the i-th layer of
reinforcement crossing that strut.

= total angular change of tendon profile

—

from tendon jacking end to point
under considerations, radians.

a s

= constant used to compute V c in slabs

and footings.

a»

= ratio of flexural stiffness of shear

head arm to surrounding composite
slab section.

« 1

= orientation of distributed

reinforcement in a strut.

«2

= orientation of reinforcement

orthogonal to a x in a strut.

= ratio of long to short dimensions:

clear span for two-way slabs, sides of
column, concentrated load or reaction

area; or sides of a footing.

= ratio of area of reinforcement cut off

to total area of tension reinforcement
at section.

8 U

= ratio of long side to short side of

A cr

concentrated load or reaction area

^fmax

the ratio of maximum factored
sustained shear within a storey to the
maximum factored shear in that
storey associated with the same load
combination.

ratio used to account for reduction of
stiffness of columns due to sustained
axial loads.

factor used to account for the effect
of the anchorage of ties on the
effective compressive strength of a
nodal zone.

factor used to account for the effect
of cracking and confining
reinforcement on the effective
compressive strength of the concrete
in a strut.

ratio of torsional stiffness of edge
beam section to flexural stiffness of a
width of slab equal to span length of
beam, center-to-center of supports.

2 Ecs^s

factor relating depth of equivalent

rectangular compressive stress block

to depth of neutral axis.

factor used to determine the fraction

of M sc transferred by slab flexure at

slab-column connections.

factor for type of prestressing

reinforcement.

0.55 for fpy/fpu not less than 0.80.
0.40 for f P y/f P u not less than °* 85 ’
0.28 for fpy/fpu not less than 0.90.
factor used to determine the portion
of reinforcement located in center
band of footing.

factor used to determine the fraction
of M sc transferred by eccentricity of
shear at slab-column connections.

1 - 7 /

: Moment magnification factor used to
reflect effects of member curvature
between ends of compression
member.

= moment magnification factor for
frames not braced against sideways,
to reflect lateral drift resulting from
lateral and gravity loads.

= design displacement, mm.

= computed, out-of-plane deflection at
mid-height of wall corresponding to
cracking moment, Af cr , mm.

= maximum deflection measured
during the second test relative to the

Association of Structural Engineers of the Philippines, Inc* (ASEP)

position of the structure at the
beginning of the second test, mm.

Af p = increase in stress i n prestressing

reinforcement due to factored loads,
MPa.

Afp S = stress in prestressing reinforcement at

service loads less decompression
stress, MPa.

Afpt = difference between the stress that can

be developed in the strand at the
section under consideration and the
stress required to resist factored
bending moment at section, M u /0,
MPa.

A max = measured maximum deflection, mm.

A n = calculated, out-of-plane deflection at

mid-height of wall corresponding to
nominal flexural strength, Af n , mm.

A 0 = relative lateral deflection between the

top and bottom of a storey due to
V us , mm.

A r = residual deflection measured 24 hours

after removal of the test load. For the
first load test, residual deflection is
measured relative to the position' of
the structure at the beginning of the
first load test. For the second load
test, residual deflection is measured
relative to the position of the
structure at the beginning of the
second load test, mm.

A rmax = measured residual deflection, mm.

A s = maximum deflection at or near

midheight due to service loads, mm

A s = out-of-plane deflection due to service

loads, mm.

A u = calculated out-of-plane deflection at

mid-height of wall due to factored
loads, mm.

A* = design storey drift of storey x , mm,

A ± = maximum deflection, during first

load test, measured 24 hours after
application of the full test load, mm.

A 2 = maximum deflection, during second

load test, measured 24hours after
application of the full test load.
Deflection is measured relative to the
position of the structure at the
beginning of second load test, mm.

£ cu = maximum usable strain at extreme

concrete compression fiber.

£ t = net tensile strain in extreme layer of

longitudinal tension reinforcement at
nominal strength, excluding strains
due to effective prestress, creep,
shrinkage, and temperature.

£ ty

X , a

ftp

<t>

= value of net tensile strain in the
extreme layer of longitudinal tension
reinforcement used to define a
compression-controlled section.

= angle between axis of stmt,
compression diagonal, or
compression field and the tension
chord of the members.

= correction factor related to unit
weight of concrete.

= modification factor to reflect the
reduced mechanical properties of
lightweight concrete relative to
normal-weight concrete of the same
compressive strength.

= modification factor to reflect the
reduced mechanical properties of
lightweight concrete in certain
concrete anchorage applications.

= multiplier used for additional
deflection due to long-term effects.

= coefficient of friction.

= number of identical arms of
shearhead.

= post-tensioning curvature friction
coefficient.

= time-dependent factor for sustained
load.

= ratio of non-prestressed tension
reinforcement.

— A s / (l w &)

= ratio of A s to bd

= ratio of compression reinforcement,

A r s to bd.

= reinforcement ratio producing
balanced strain conditions.

- ratio of area of distributed
longitudinal reinforcement to gross
concrete area perpendicular to that
reinforcement.

= ratio of prestressed reinforcement,
Ap S t o bd p .

= ratio of volume of spiral
reinforcement to total volume of core
confined by the spiral, measured out-
to-out of spirals.

= ratio of area of distributed transverse
reinforcement to gross concrete area
perpendicular to that reinforcement.

= ratio of tie reinforcement area to area
of contact surface.

= in

b v s

= ratio of tension reinforcement, A s to

b w d.

= strength-reduction factor.

National, Structural Code of the Philippines Volume E ditto r

4-20 CHAPTER 4 - Structural Concrete

/ T cr
T uncr

*l>cp,N

$cp,Na

tyc.P
*1* c.V

*l>e
\ Pec,N
^ Pec,Na

tyecy

V'ed.JV

*Ped,Na

M*edy

tyhy

= stiffness reduction factor.

= characteristic bond stress of adhesive
anchor in cracked concrete, MPa.

= characteristic bond stress of adhesive
anchor in uncracked concrete, MPa.

= factor used to modify development
length based on cover.

= factor used to modify tensile strength
of anchors based on presence or
absence of cracks in concrete.

= factor used to modify tensile strength
of post-installed anchors intended for
use in uncracked concrete without
supplementary reinforcement to
account for the splitting tensile
stresses due to installation.

= factor used to modify tensile strength
of adhesive anchors intended for use
in uncracked concrete without
supplementary reinforcement to
account for the splitting tensile
stresses due to installation.

= factor used to modify pullout strength
of anchors based on presence or
absence of cracks in concrete.

= factor used to modify shear strength
of anchors based on presence or
absence of cracks in concrete and
presence or absence of
supplementary reinforcement.

= factor used to modify development
length based on reinforcement
coating.

= factor used to modify tensile strength
of anchors based on eccentricity of
applied loads.

= factor used to modify tensile strength
of adhesive anchors based on
eccentricity of applied loads.

= factor used to modify shear strength
of anchors based on eccentricity of
applied loads.

= factor used to modify tensile strength
of anchors based on proximity to
edges of concrete member.

= factor used to modify tensile strength
of adhesive anchors based on
proximity to edges of concrete
member.

= factor used to modify shear strength
of anchors based on proximity to
edges of concrete member.

= factor used to modify shear strength
of anchors located in concrete
members with h a < 1.5c al .

= factor used to modify development

length based on confining
reinforcement.

= factor used to modify development
length based on reinforcement size.
xf) t = factor used to modify development

length for casting location intension.
if> w = factor used to modify development

length for welded deformed wire
reinforcement in tension.

Q o = amplification factor to account for

overstrength of the seismic-force-
resisting system determined in
accordance with the general building
code.

a) w , a) pw , o)' w = reinforcement indices for flanged
sections computed as for g>, 0) p and
o) f except that b shall be the web
width, and reinforcement area shall
be that required to develop
compressive strength of web only.

402.3 Terminology

ADHESIVE are chemical components formulated from
organic polymers, or a combination of organic polymers
and inorganic materials that cure if blended together.

ADMIXTURE is a material other than water, aggregate,
or hydraulic cement used as an ingredient of concrete and
added to concrete before or during its mixing to modify
its properties.

AGGREGATE is a granular material, such as sand,
gravel, crushed stone and iron blast-furnace slag, and
when used with a cementing medium forms a hydraulic
cement concrete or mortar.

AGGREGATE, LIGHTWEIGHT is an aggregate
meeting the requirements of ASTM C330 and having a
bulk density with a dry, lose weight of 1 120 kg/m 3 or
less, determined in accordance with ASTM C29. In some
standards, the term lightweight aggregate is being
replaced by the term low-density aggregate.

ANCHOR is a steel element either cast into concrete or
post-installed into a hardened concrete member and used
to transmit applied loads to the concrete.

ANCHOR, CAST-IN is a headed bolt, headed stud, or
hooked bolt (J- or L-bolt) installed before placing
concrete.

ANCHOR, HEADED BOLT is a cast-in steel anchor
that develops its tensile strength from the mechanical
interlock provided by either a head or nut at the embedded
end of the anchor.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHAPTER 4 - Structural Concrete

4 21

ANCHOR, HOOKED BOLT is a cast-in anchor
anchored mainly by bearing of the 90-degree bend (L-
bolt) or 180-degree bend (J-bolt) against the concrete, at
its embedded end, and having a minimum e ^ equal to

3 d a .

ANCHOR, HEADED STUD is a steel anchor
conforming to the requirements of AWSD1.1M and
affixed to a plate or similar steel attachment by the stud
arc welding process before casting.

ANCHOR, HORIZONTAL OR UPWARDLY
INCLINED is an anchor installed in a hole drilled
horizontally or in a hole drilled at any orientation above
horizontal.

ANCHOR, POST-INSTALLED, is an anchor installed
in hardened concrete; adhesive, expansion, and undercut,
anchors are examples of post-installed anchors.

ANCHOR, ADHESIVE is a post-installed anchor,
inserted into hardened concrete with an anchor hole
diameter not greater than l.Stimes the anchor diameter,
that transfers loads to the concrete by bond between the
anchor and the adhesive, and bond between the adhesive
and the concrete.

ANCHOR, ADHESIVE-STEEL ELEMENTS are steel
elements for adhesive anchors include threaded rods,
deformed reinforcing bars, or internally threaded steel
sleeves with external deformations.

ANCHOR, EXPANSION is a post-installed anchor,
inserted into hardened concrete that transfers loads to or
from the concrete by direct bearing or friction or both.

ANCHOR, UNDERCUT is a post-installed anchor that
develops its tensile strength from the mechanical interlock
provided by undercutting of the concrete at the embedded
end of the anchor. Undercutting is achieved with a special
drill before installing the anchor or alternatively by the
anchor itself during its installation.

ANCHOR GROUP is a number of similar anchors
having approximately equal effective embedment depths
with spacing s between adjacent anchors such that the
protected areas overlap.

ANCHOR PULLOUT STRENGTH is the strength
corresponding to the anchoring device or a major
component of the device sliding out from the concrete
without breaking out a substantial portion of the
surrounding concrete.

ANCHORAGE DEVICE in post-tensioned members, the
hardware used to transfer force from prestressed
reinforcement to the concrete.

ANCHORAGE DEVICE, BASIC MONOSTRAND is

an anchorage device used with any single strand or a
single 16mm. or smaller diameter bar that is in accordance
with Sections 425.8.1,425.8.2 and 425,9.3.1a.

ANCHORAGE DEVICE, BASIC MULTISTRAND is

an anchorage device used with multiple strands, bars, or
wires, or with single bars larger than 16 mm diameters
that satisfies Sections 425.8.1, 425.8.2 and 425.9.3.1b.

ANCHORAGE DEVICE, SPECIAL is an anchorage
device that satisfies tests required in Section 425.9.3.1c.

ANCHORAGE ZONE in post-tensioned members,
portion of the member through which the concentrated
prestressing force is transferred to the concrete and
distributed more uniformly across the section; its extent is
equal to the largest dimension of the cross section; for
anchorage devices located away from the end of a
member, the anchorage zone includes the disturbed
regions ahead of and behind the anchorage device.

ATTACHMENT is a structural assembly, external to the
surface of the concrete that transmits loads to or receives
loads from the anchor.

B-REGION is a portion of a member in which it is
reasonable to assume that strains due to flexure vary
linearly through section.

BASE OF STRUCTURE is a level at which the
horizontal earthquake ground motions are assumed to be
imparted to a building. This level does not necessarily
coincide with the ground level.

BEAM is a member subjected primarily to flexure and
shear, with or without axial force or torsion; beams in a
moment frame that forms part of the lateral-force-resisting
system are predominantly horizontal members; a girder is
a beam.

BOUNDARY ELEMENT is a portion along wall and
diaphragm edge, including edges of openings,
strengthened by longitudinal and transverse
reinforcement.

BUILDING OFFICIAL is a term used in a general
building code to identify the person charged with
administration and enforcement of provisions of the
building code. Such term as building inspector is a
variation of the title, and the term “building official” as

ISpoinea Volume } V 7 U ‘ Edition, 2015

4-22 CHAPTER 4 - Structural Concrete

used in this Code, is intended to include those variations,
as^ell as others that are used in the same sense.

CEMENTITIOUS MATERIALS are materials that
have cementing value if used in concrete either by
themselves, such as portland cement, blended hydraulic
cements, and expansive cement, or such materials in
combination with fly ash, raw or other calcined natural
pozzolans, silica fume, and slag cement.

COLLECTOR is an element that acts in axial tension or
compression to transmit forces between a structural
diaphragm and a vertical element of the seismic-force-
resisting system.

COLUMN is a member, usually vertical or predominantly
vertical, used primarily to support axial compressive load,
but that can also resist moment, shear, or torsion. Columns
used as part of a lateral-force-resisting system resist
combined axial load, moment, and shear. Refer to moment
frame.

COLUMN CAPITAL is an enlargement of the top of a
concrete column located directly below the slab or drop
panel that is cast monolithically with the column.

COMPLIANCE REQUIREMENTS is a construction-
related Code requirements directed to the contractor to be
incorporated into construction documents by the licensed
design professional, as applicable.

COMPOSITE CONCRETE FLEXURAL MEMBERS

are concrete flexural members of precast or cast-in-place
concrete elements, constructed in separate placements but
connected so that all elements respond to loads as a unit.

COMPRESSION-CONTROLLED SECTION is a

cross section in which the net tensile strain in the extreme
tension reinforcement at nominal strength is less than or
equal to the compression-controlled strain limit.

COMPRESSION-CONTROLLED STRAIN LIMIT is

a net tensile strain at balanced strain conditions.

CONCRETE are mixture of portland cement or any other
hydraulic cement, fine aggregate, coarse aggregate and
water, with or without admixtures.

CONCRETE, ALL-LIGHTWEIGHT is a lightweight
concrete containing only lightweight coarse and fine
aggregates that conform to ASTM C330.

CONCRETE, LIGHTWEIGHT is a concrete
containing lightweight aggregate and an equivalent
density, as determined by ASTM C567, between 1440
and 1840 kg/m 3 .

CONCRETE, NON-PRESTRESSED is a reinforced
concrete with at least the minimum amount of non-
prestressed reinforcement and no prestressed
reinforcement; or for two-way slabs, with less than the
minimum amount of prestressed reinforcement.

CONCRETE, N ORM ALWEIGHT is a concrete
containing only aggregate that conforms to ASTM C33.

CONCRETE, PLAIN is a concrete with no
reinforcement or with less reinforcement than the
minimum amount specified for reinforced concrete.

CONCRETE, PRECAST is a concrete element cast
elsewhere than its final position in the structure.

CONCRETE, PRESTRESSED is a concrete in which
internal stresses have been introduced to reduce potential
tensile stresses in concrete resulting from service loads.

CONCRETE, REINFORCED is a concrete reinforced
with at least the minimum amounts of non-prestressed or
prestressed reinforcement required by this Code.

CONCRETE, SAND-LIGHTWEIGHT is a concrete
containing only normal weight fine aggregate that
conforms to ASTM C33M and lightweight coarse
aggregate that conforms to ASTM C330M.

CONCRETE, STEEL FIBER-REINFORCED is a

concrete containing a prescribed amount of dispersed,
randomly oriented, discontinuous deformed steel fibers.

concrete Strength, specified

COMPRESSIVE is a compressive strength of concrete
used in design and evaluated in accordance with
provisions of this Code, MPa. Whenever the quantity f c
is under a radical sign, square root of numerical value
only is intended, and result has units of MPa.

CONCRETE BREAKOUT STRENGTH is a strength
corresponding to a volume of concrete surrounding the
anchor or group of anchors separating from the member.

CONCRETE PRYOUT STRENGTH is a strength
corresponding to formation of a concrete spall behind
short, stiff anchors displaced in the direction opposite to
the applied shear force.

CONNECTION is a region of a structure that joins two
or more members; a connection also refers to a region that
joins members of which one or more is precast.

CONNECTION, DUCTILE is a connection that
experiences yielding as a result of the earthquake design
displacements.

Association of Structural Engineers of the Philippines, Inc. (ASEP)

CHART ER 4 - Structural Concrete

T 23

CONNECTION, STRONG is a connection between
one or more precast elements that remains elastic while
adjoining members experience yielding as a result of the
earthquake design displacements.

CONTRACT DOCUMENTS is a written and graphic
documents and specifications prepared or assembled for
describing the location, design, materials, and physical
characteristics of the elements of a project necessary for
obtaining a building permit and construction of the
project.

CONTRACTION JOINT is a formed, sawed, or tooled
groove in a concrete structure to create a weakened plane
and regulate the location of cracking resulting from the
dimensional change of different parts of the structure.

COVER, SPECIFIED CONCRETE is a distance
between the outermost surface of embedded
reinforcement and the closest outer surface of the
concrete.

CROSSTIE is a continuous reinforcing bar having a
seismic hook at one end and a hook not less than 90-
degree hooks with at least six-diameter extension at the
other end. The hooks shall engage peripheral longitudinal
bars. The 90-degree hooks of two successive crossties
engaging the same longitudinal bars shall be alternated
end for end,

D-REGION is a portion of a member within a distance,
h , from a force discontinuity or a geometric discontinuity

DESIGN DISPLACEMENT is a total calculated lateral
displacement expected for the design-basis earthquake.

DESIGN INFORMATION is project-specific
information to be incorporated into construction
documents by the licensed design professional, as
applicable.

DESIGN LOAD COMBINATION is a combination of
factored loads and forces.

DESIGN STOREY DRIFT RATIO is a relative
difference of design displacement in between the top and
bottom of a storey, divided by the story height.

DEVELOPMENT LENGTH is a length of embedded
reinforcement, including prestressing strand, required to
develop the design strength of reinforcement at a critical
section.

DISCONTINUITY is an abrupt change in geometry or
loading.

DISTANCE SLEEVE is a sleeve that encases the center
part of an undercut anchor, a torque-controlled expansion
anchor, or a displacement-controlled expansion anchor,
but does not expand.

DROP PANEL is a projection below the slab used to
reduce the amount of negative reinforcement over a
column or the minimum required slab thickness, and to
increase the slab shear strength.

DUCT is a conduit, plain or corrugated, to accommodate
prestressing reinforcement for post-tensioning
applications.

DURABILITY is an ability of a structure or member to
resist deterioration that impairs performance or limits
service life of the structure in the relevant environment
considered in design.

EDGE DISTANCE is a distance from the edge of the
concrete surface to the center of the nearest anchor.

EFFECTIVE DEPTH OF SECTION is a distance
measured from extreme compression fiber to centroid of
tension reinforcement.

EFFECTIVE EMBEDMENT DEPTH is an overall
depth through which the anchor transfers force to or from
the surrounding concrete; effective embedment depth will
normally be the depth of the concrete failure surface in
tension applications; for cast-in headed anchor bolts and
headed studs, the effective embedment depth is measured
from the bearing contact surface of the head.

EFFECTIVE PRESTRESS is a stress remaining in
prestressing reinforcement after all losses in Section
420.3.2.6 have occurred.

EMBEDMENTS is an items embedded in concrete,
excluding reinforcement as defined in Section 420 and
anchors as defined in Section 417. Reinforcement or
anchors welded, bolted or otherwise connected to the
embedded item to develop the strength of the assembly are
considered to be part of the embedment.

EMBEDMENTS, PIPE is an embedded pipes, conduits,
and sleeves.

EMBEDMENT LENGTH is a length of embedded
reinforcement provided beyond a critical section.

EQUILIBRIUM DENSITY is a density of lightweight
concrete determined in accordance with ASTMC 567
after exposure to a relative humidity of 50 ± 5 percent and
a temperature of 23 ± 2.00 °C for a period of time
sufficient to reach constant density.

National Structural Code of the Philippines Volume 1

4-24 CHAPTER 4 - Structural Concrete

EXPANSION SLEEVE is an outer part of an expansion
anchor that is forced outward by the center part, either by
applied torque or impact, to bear against the sides of the
predrilled hole. Refer to anchor, expansion.

EXTREME TENSION REINFORCEMENT is a layer
of prestressed or non-prestressed reinforcement that is the
farthest from the extreme compression fiber.

FINITE ELEMENT ANALYSIS is a numerical
modeling technique in which a structure is divided into a
number of discrete elements for analysis.

FIVE PERCENT FRACTILE is a statistical term
meaning 90 percent confidence that there is 95 percent
probability of the actual strength exceeding the nominal
strength.

HEADED DEFORMED BARS is a deformed
reinforcing bars with heads attached at one or both ends.

HEADED SHEAR STUD REINFORCEMENT is a

reinforcement consisting of individual headed studs or
groups of studs, with anchorage provided by a head at
each end, or by a head at one end and a common base rail
consisting of a steel plate or shape at the other end.

HOOP is a closed tie or continuously wound tie. A closed
tie, made up of one or several reinforcement elements,
each having seismic hooks at both ends. A closed tie shall
not be made up of interlocking headed deformed bars.
Section 425.7.4.

INSPECTION is an observation, verification, and
required documentation of the materials, installation,
fabrication, erection or placement of components and
connections to determine compliance with construction
documents and referenced standards.

INSPECTION, CONTINUOUS is the full time
observation, verification, and required documentation of
work in the area where the work is being performed.

INSPECTION, PERIODIC is the part-time or
intermittent observation, verification, and required
documentation of work in the area where the work is
being performed.

ISOLATION JOINT is a separation between adjoining
parts of a concrete structure, usually a vertical plane, at a
designed location such as to interfere least with
performance of the structure* yet such as to allow relative
movement in three directions and avoid formation of
cracks elsewhere in the concrete and through which all or
part of the bonded reinforcement is interrupted.

JACKING FORCE In prestressed concrete, temporary
force exerted by device that introduces tension into
prestressing reinforcement.

JOINT is a portion of structure common to intersecting
members.

LICENSED DESIGN PROFESSIONAL is an
individual who is licensed to practice structural design as
defined by the statutory requirements of the Professional
Regulation Commission (PRC) or jurisdiction in which
the project is to be constructed and who is in responsible
charge of the structural design.

LOAD are forces or other actions that result from the
weight of all buildin

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